All British citizens require a tourist visa to enter Nepal, which you can apply for in person at the Nepalese Embassy in London, by post (allow 2-3 weeks), or on arrival in Kathmandu airport. A 15-day tourist visa currently costs £20 (the 15 days start from the date of arrival in Nepal). You can find full details, including an application form that you can print out if applying by post or what is required if obtaining a visa on arrival, at
uk.nepalembassy.gov.np. As well as having a visa, you must ensure that your passport is valid for a further six months from the date of entry into Nepal and that it has at least 1 blank page. If you or any member of your party is not a British citizen or holds a non-British passport, you should check passport and visa requirements.