I heartily recommend 'O2' - after being messed around and let down by Orange for ages.
the £12.50 monthly fee drops to £ 7.50 per month, if you are willing top up an O2 enabled mobile with £ 10 every 3 months.
Free phone calls to O2 - 24hrs a day 365 days a year e.t.c. ( including technical ) - which Orange where charging a fortune for , just for me to repeatedly ask / chase why my line kept dropping from 'slow' to 'extra slow' . At best orange gave me 1.6 Meg , which dropped ( without appology on their part ) to 1 Meg, then 0.5 Meg.
When cornered, all their technical team could say was " we probaly put something big like a local school on the same exchange " - as if the inadequacy of their infrastructure was my responsibility - and not theirs for expanding capacity / servers! At one stage, I only got any service from them when a techy mate hammered into some far flung European 'Orange' file servers for me . They even blamed B.T. phone lines for the dramatic and permanent drop in speed ; a falacy quickly revealed when O2 pumped 4.2 Meg straight through the same exchange / line a few days later.
For £7.50 a month, O2 is giving me a consistent 4 Meg . Also the 'free to call' and genuinely helpfull call centres are in Leeds and Glasgow - not someone , somewhere thousands of miles away reading from a script all the time, and being largely hard to understand or be willing to deviate from that script.
I know a local chap who has put his entire Business and personal lines through O2 - and he has found that they have always been great at ( freely ) advising on technical matters and working out nice deals for flexible circumstances.
Orange cost me a fortune in calls and stress. Just wish I had have opted out sooner.
End of rant. :)