You can use ISDN. The cheapest option is BT Home Highway or ISDN-2e which is about £30 a month and gives you 2x64K channels which can be bonded (depending on yout ISP) to a single 128K channel.
On top of that you will have the BT telephone charges - or go for Surftime which will add about £7.00 per month for Evening & Weekends or £25.00 per month anytime.
Not as good as ADSL I'm afraid.