I have had the same problem neil, I bet you love talking to the technical support as well ;)
the reality is that there are too many users for the exchange, the exchange needs to be completely updated, the line drops you get is because of the sheer volume of broadband users, they cannot fix this problem and everyone I know has the same prob.
its a big prob for BT as it would cost a looot of money to improve the service, I have terminated my contract with them because of this. I now have virgin cable (it has to be a cable connection because internet providers like sky only rent the line of BT so you would still get the probs)
virgin cable broadband is very good, no loss of service and cheaper than BT, you dont have to have the tv,phone or anything just the broadband. you may consider it when you are fed up with indian technical help, engineers who say there is nothing wrong or when you keep losing your connection.