Leased lines are seriously expensive beasts, and normally business grade, which means speed, reliability and cost reflect that.
What is it you are specifically trying to achieve with a leased line solution?
If you can get FTTC with a TalkTalk backhaul, I would seriously be looking at the Andrews and Arnold Home::1T (terabyte) packages which clock in from £60/month. Full 80/20 provisioned service over the TT backhaul network, but actual speed dependent on line length of course.
http://www.aaisp.net.uk/broadband-home1-terabyte.html
To me, this would be like an entry level leased line, but more at a consumer (non-business) level. They even do a SoHo version of this graded for 2 terabytes per month.
If you exceed your quota, your connection is limited down to 3Mb/s (6Mb/s on the SoHo version) until the start of the next month, so your connection is never abruptly terminated, just slowed down.
Edited by deleted (Wed 30-Mar-16 15:23:27)