Based on your postcode/company telephone number (from the Multimap link provided and your website) you're serviced by the Locks Heath BT exchange which appears to be ~3km as the crow flies from the location linked to. However due to physical routing you may find the actual line length is closer to 5-6km which is about the limit of an ADSL line.
I also did some sleuthing based on the address of your company and your neighbours on the same site as your premises (Universal Marina). Using Universal Marina's telephone number (also most likely supplied from the same BT DP) you may get up to 1Mb ADSL Max or 512kb fixed rate (1Mb fixed rate is reported as amber in the RAG info).
I suspect that the cable route back to the exchange will go via Sarisbury, Bridge Road and Park Gate which is why the line length is so long and hence the limited speed.
I doubt that local re-routing/replacement of the line would have any effect. I also doubt that if BT could dig a new route to a DP closer to the exchange it'd be economically viable. Judging by the aerial photo's there are lots of properties probably well serviced by existing infrastructure with existing wayleave agreements etc.
Your other options -
Satellite - as you mentioned is going to have latency issues, but you can get services such as tooway (provided by Eutelsat) that provide two way access via satellite.
Wireless - unless you have a local WiMAX/Mesh Radio provider in your area then you'd need to build your own infrastructure so that you have an ADSL service terminating in a building closer to the exchange, and beam the signal (via say microwave or other line of sight technology) back to your premises. This is expensive to do.
Leased line type service (E1, Megastream) - may not be possible due to distance from the exchange, also it's in a whole different pricing world from ADSL....think £000's of pounds a year.
3G/mobile broadband - Three seem to have fairly good coverage where you are. For about £20 a month you can have up to 15GB data transfer and speeds up to 3.6Mb. You can also get one of these: Huawei D100 Router to allow you share the connection. I'm using one of these over in Donegal, Ireland out in the boonies where the service is rated at OK for outdoor use and it works just fine indoors.
But perhaps your best option is probably to investigate a bonded ADSL service from company that specialises in this type of service.