I used this company for over a year now and all has been as they state.
They work on the 3 Network. Not sure where you can topup locally but you can do it online
From their website
"New Pay As You Go SIM for lowest cost and premium quality International and UK Calls
StanMobile Pay As You Go SIM Card is the best way to make International and UK calls directly from your mobile. Currently we are offering cheapest rates for International calls starting from 3p per minute. Also with StanMobile you will have lowest ever UK Rates of 2p per minute for UK Landline, 7p per minute for UK Mobile (Any Network, Any Time) and 10p per SMS (both UK & International).
If that is not enough we are offering unlimited*, high speed mobile broadband on the same SIM Card for £9.99 a month with no contracts, no setup fees and no maintenance charges.
*Subject to fair use policy of 1GB per month
StanMobile – For Every Second
StanMobile offers 100% per second billing for our customers so that you will get charge only exact second rather than per minute and rounded to the nearest.
StanMobile – For 3 Way Use
StanMobile is now introducing 3 WAY USE Topup card to our value customer.
• From StanMobile SIM
• Share Your Credit with Family and Friends
• From Local and Free Phone Access"