You might want to check out smaller ISPs like AAISP, uno, IDNet, CIX, Aquiss and perhaps Zen Internet. Aside from Zen, their offers aren't always structured in the same way as large ISPs*, but their contracts are usually 12 months, typically there's no in-fixed term price rises with these companies, so there's little point in waiting for the majors to complete their competition-law-challenging increases - in fact if you wanted to use these perhaps better to do it before the big ISP's dust settles. This is worth a read.
These smaller suppliers tend to major on better customer service, so their average cost to you will probably be slightly higher than you'd get out of large ISPs if you haggle or switch regularly, but at least you're not on the hook for unavoidable and outrageous RPI + 4% increases that will be much bigger for those with a discounted contract.
Something else to consider is moving your landline to a VOIP provider and buying your own VOIP adaptor. That means that the line is independent of the broadband, and opens up all manner of interesting possibilities, everything from automatic call recording, advanced forwarding and filtering, using an established UK landline number from anywhere in the world. Note that if you're going for a bare bones VOIP product there's a short but steep learning curve in doing this. My landline is now a VOIP product with Andrews & Arnold, on a pay as you use basis and £1.44 a month line rental, other VOIP providers offer bundled "free" calls and some provide the equipment, but with higher monthly charges. Vonage are worth considering if you want a packaged product that largely works out of the box.
* For example, with Aquiss you have to supply your own router or mesh wifi system - that actually suits me, but won't suit everybody.
