Fiick me, you lot pay a lot for your contracts
I pay £7.50 a month for I think its 9Gb, unlimited texts, though only 250 mins. That with Evil Everywhere on a 30 day rolling contract.
EE has by far the best coverage - hence wins every independent award (much to the annoyance of that silly tart who, fortunately, has left OFCOM) - though O2/Voda have better 2G/3G penetration indoors (EE and Three have crap frequencies for indoor penetration). Note, 4G cannot natively carry voice, and not all providers allow VoLTE (effectively Voice over a 4G data connection) on all contracts.
I use NiffNaff as a backup SIM, as it runs on O2, which is usually the next best network, though in cities I'd argue Voda might just pip them. NiffNaff starts at £6 for 500Mb, ultd texts and calls, rising to £20 for 80Gbb (or £25 for unlimited data, but throttled at peak when over 80Gb is used)
I plonked on a £25 goodybag on my NiffNaff SIM when I was up in Scotland, as O2 worked in the cottage, and the broadband was rubbish. I must have uploaded well over 100Gb to gaytube in that month. Oops