You can buy them easily from the airport too (especially coming into the UK). Changing wifi settings is not needed - it is still 2.4ghz, the standard only changes the power levels. If it works in the US it will work in the UK.
For more geeky things, the welcome trust (featuring victorian medical curiosities like darwin's walking cane, a mummified south american, mad king george's hair, 19th century japanese sex toys, etc) and the british library treasures room (featuring the magna carta, gutenburg bible, domesday book, early maps, da vinci notes, shakespeare, beatles, etc) are great and are practically next door to each other. Most locals dont even know about them but they are definitely worth half a day or so between them.