If 3G/4G can provide the worst case backup then it sounds like you are some way from the need for full leased line redundancy.
Just to be a little careful here, many phone operators use BT backhaul as well.
We experienced an outage in Birmingham
, event taking out EFM and leased BT fibre. Critical systems had a failover of 3G/4G, we found EE and Three also use BT. The only option we can think of is Virgin Media, but that's a 18 month lead time for install just like a BT leased line. May install microwave to shoot over 10km to a Virgin Media for a few customers.
Edited by loadbang (Thu 22-Sep-16 21:12:39)