I can't shed any light on your specific problem, I've had Android phones for a long time and don't have any problems, but I do generally have a good 3G signal. Do any of the other mobile firms have good 3G coverage in your area? There are only four mobile network operators in the UK (mentioned below), all the others piggy back off those 4, you can find further info
here.
Just reading what Kitz posted reminded me that your phone may keep trying to swap to 3G then drop back to 2G, I think there may well be a setting somewhere to set it to 2G only.
£1 a day for 25MB sounds like it could be very expensive way of using your phone, there are now some very good Sim only deals out.
Vodafone 300 minutes, 500 texts, 250MB data for £9 a month
Three 200 minutes, 5000 texts, 500MB data for £6.90 - I'm on the One Plan, 2000 minutes, 5000 texts and unlimited data with tethering for £15, but looks like it's gone up to £20 a month
Orange 500 minutes, 500 texts, 100MB data £8 a month
O2 100 minutes, unlimited texts, 100MB data £8 a month
Those above are the cheapest tariffs for 12 month contract, a little more money can get some good allowances, tie that in with a cash back deal and you can have a good contract at a very good rate. Do some in depth research and it is possible to get some very good deals.