Aviatrix

Her Majesty's airport officials have no problems with minors entering the country without their parents. Thousands and thousands of youngsters travel to the UK every year, without their parents, to stay with host families and attend language classes. And I've had visits from several under-age relatives over the years - they all had letters from their parents but in most cases weren't even asked to show them.

However, having said all that I would echo the advice given by others - check with the British Embassy/Consulate to find out exactly what's required. Also (and I really hate having to say this) there is quite a bit of paranoia in British society (more than in many other countries) about female youngsters travelling with adult males, so prepare yourself for the possibility of being treated with suspicion both by Immigration and by staff at hotels.