The currency of Britain is the pound sterling (£). Paper money ('notes') comes in £5, £10, £20 and £50 denominations. Some shops don't accept £50 notes because fakes circulate.
Other currencies are very rarely accepted, except at some gift shops in London, which may take euros, US dollars, yen and other major currencies.
Restaurants Around 10% in restaurants and teahouses with table service. Nearer 15% at smarter restaurants. Tips may be added to your bill as a 'service charge'. However, paying tips or the service charge is not compulsory – it's up to you.
Pubs & Bars If you order drinks (or food) and pay at the bar, tips are not expected. If you order at the table and your meal is brought to you, then 10% is usual.
Taxis Usually around 10%, or rounded up to the nearest pound, especially in London.