you don't seem to have checked whats available at your exchange (not all services are available everywhere), use the link
here to see which llu services (if any) are available. the sky/be/o2 llu options do look very good if available to you, and if you don't mind long contracts, if they aren't then questions about your expected usage arise (Gb/month). post the answers back here.
just realised you'd possibly be changing from cable to bt line (new 12 month contract), i may be wrong, but i think if you then go with a LLU supplier you'll incur a hefty charge from BT (~�170), which could still work out cheaper than the alternatives.
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