British Roads
British Roads are considered some of the best in the world, although, unless you specifically looked, they share a lot of similarities with the roads of any other industrial nation.
Probably the biggest difference between British Roads and those in the rest of the world (except for Japan, Indonesia, Ireland and a few Commonwealth nations, such as India, Australia and South Africa) is that we drive on the left almost everywhere - the only exception is the short road outside the Savoy Hotel. This is probably said to be a hangover from the days of highwaymen, as riding on the left makes it easier for a right-handed person to draw a sword or fire a pistol if some ruffian in the middle of the road tries to waylay them. Interestingly as most people are right-eye dominant it lets modern motorcar uses see oncoming traffic better, resulting in very very slightly lower head on collisions than right-hand drive nations.
Every public road in the UK is paved, including the majority in the countryside. Road signs are also very common, and the heavily standardised design means that they are recognisable instantly - the only exceptions are the fingerposts sometimes seen in traditional villages. These may require that drivers slow down or even stop to fully take in the directions. In addition to universal paving, expect to see cats-eyes (spring retractable self-cleaning reflective lane separation indicators) on all but the smallest roads and street lights in even quite small villages.
Motorways in Britain are similar to freeways or autobahns - other, less busy, roads that Americans would describe as "highways" are generally called A-roads - less major roads are then B-roads. C and D roads technically exist as well, but nobody labels them (they are usually just referred to as "unclassified". Particularly major A roads are referred to as "Trunk Roads", and are under national control rather than local. Many of the Trunk Roads follow the routes of former Roman Roads (see below). Other than Motorways which have their own sets of rules, there is very little standardisation between the types of roads, for example in terms of width, lighting, kerbing etc, other than that outside of urban areas, most dual carriageways are A roads (although not all A roads or even trunk roads are dual carriageway).
Speed limits in the UK are generally 30 mph in built up areas, 60 mph on single carriageways and 70 mph on dual carriageways (roads with a central reservation) and motorways, but lorries and buses have lower limits than this, and driving slower is often wise on tight country lanes. British roads are some of the safest in the world, this having been achieved by means of policing, road engineering and driver education. These measures resulted in a steady fall in the accident rate year on year, until the desire to save money led to the replacement of traffic police with automated enforcement of very restrictive speeding regulations; a great many country and city roads will have speed cameras, which can issue both a fine and add penalty points to a license. Associated propaganda led to a belief that you were a safe driver as long as you kept below the limit, no matter how incompetent you were at other aspects of driving, while the reduction in actual policing led to incompetent and dangerous driving going largely unchecked, and the accident rate ceased to fall. Recently the backlash among motorists against automated speeding enforcement has led to the removal of speed cameras in some areas, and these areas are now again seeing a reduction in accident rates. Light up signs telling you to slow down if you approach them at more than the speed limit are becoming popular commonplace as well, and Average Speed Monitoring coupled with CCTV and license plate-recognition technology is being rolled out across the major motorways. Likewise, expect no sympathy if a Traffic Warden catches you parked on yellow lines, or stopped on red ones, which in central London may as well be a hanging offence as far as some are concerned.
There's an ongoing argument about whether the motorway speed limit should be raised to 80 or 90 mph. Argument for: some people drive that fast anyway, and the 70 mph limit was introduced when ordinary cars couldn't manoeuvre safely above that speed. Argument against: it might encourage speeding. A significant number of senior police officers favour an increase to 80 mph on motorways.
With the rise in eco-friendly transport, many roads now have divided areas for other traffic - most large towns have bus lanes, taxi lanes or tram lanes, and cycle lanes are common in suburban and semi-rural areas. These are marked with heavy lines and usually filled with red tarmac. There are also lots of speed bumps and chicanes in the suburbs. Modern traffic calmers generally consist of a small beveled square in the road - positioning your car over the middle usually reduces the bump, especially if you have a wide car. The idea behind this is that ambulances and fire engines pass over the bump without noticing it; they're also reckoned to be safer for cyclists, who can skirt round them.
The British road network, thematically appropriate for a country that enjoys living in the past, is essentially based on what was laid down by the Romans nearly two thousand years ago. The A1, the main north/south artery, almost entirely follows the path of Ermine Street, the main Roman road. As Dave Gorman noted, this means that it's very easy to go up and down in Britain but much harder to go from side to side (only about two motorways run east/west in any meaningful way), although in Wales it is easier to go side to side, meaning that if you want to get from Cardiff to Bangor it's probably faster to take the M4 into England, head north on the English motorways, and head west at the level of Liverpool. And quite major cities may not be connected to the most developed part of the network, because they were only villages in 120 AD.
You have to pay an annual tax to own a car (unless you get an certificate stating it's being stored off-road), which is now based on CO2 emissions. If your car is older than three years, it has to have an annual inspection, called an MOT (Ministry of Transport) test, to allow you to drive it. The Government, in a further attempt to reduce carbon emissions keep the British Far Eastern car industry in business, has recently introduced a scheme where they'll pay you £2,000 to scrap your car if it's over 10 years old.
All vehicles (with a few exceptions) allowed to run on British roads must also have an annual MOT test once they reach 3 years old. This is often falsely viewed as a redundant acronym, as people assume "T" stands for test. It does not, MOT stands for Ministry Of Transport, the organisation that first introduced the tests (this week known as the Department for Transport). The test basically ensures that the vehicle is in a fit state to be on the roads, although has since introduced become much stricter and now includes such as emissions. One interesting point about the MOT is that a vehicle only has to comply to the standards of the time it was first registered, not of the present day, meaning that sufficiently old card do not need modern frippery like seat belts or indicators.
Like other European roads, British roads tend to be narrower and smaller than American ones.
Car Registrations
The UK has undergone a number of different registration systems in the automobile history. If you know this system, you can understand a lot about a character.
The dashes below are for ease of reading and do not appear on license plates.
1904-1932
One or two letter region code- a number from 1 to 9999
1932-1953
Three letter region code - number from 1 to 9999
- Stroke Country still uses this system
1953-1963
Number from 1 to 9999 - Three letter region code.
1963 to 1983
Three letter region code - Number from 1 to 999 - Year code (A= 1963, B= 1964, etc, skipping a few letters)
1983-2001
Year code - Number from 1 to 999 - Region code
From 1998, the year code changed twice a year.
2001-present
The current system goes something like this.
Two letter region code - Year number (if registered Mar-Sept) or Year Number plus 50 (Sept-Mar) - Three random letters (provided they are not rude).
The system started with 51 and is currently on 10. An example of a registration would be LC 58 RFD, indicating a London-registered car from the second half of 2008/9.
As of 2010, the numberplates will go 10 and 60 instead of 00 and 50, so a car made in the second half of 2012 will bear the year-number 62.
I, J, Q, T, U and Z are not included in the region codes. A car beginning with Q does not have an easily determinable age.
Private registrations and personalised plates
Don't be such a twat. Considered a sign of possessing extreme vanity and too much money, but available for a fee if you really insist. However, the registration numbers of any car that appeared regularly on television are not for sale, lest someone try to pass another car of similar make off as the (presumably now non-existent) genuine prop. Your mileage may vary on the acceptability of these. Some may simply be a normal looking plate that happens to have the owners initials, which are normally accepted as being a personal thing (after all, only people who know your name will tell anyway). The more obvious and flashy the personalised plate is, the less acceptable it tends to be. Many will even make changes to the font or spacing to make the plate read differently to what it says. This can make figuring out what the actual registration of the car is very difficult, and hence is not only widely looked down on, but also illegal. Buses and coaches may also carry these numbers, usually to hide the age of the vehicle but sometimes for the same reasons above. These plates can also be Northern Irish plates, which don't carry a year identifier and can be transferred without regard for vehicle age.