You must arrange any visit to Bhutan through an authorised travel agent well in advance. See Entry requirements.
Britain is represented in Bhutan by an Honorary Consul. Consular support is not available from the British government in Bhutan. However, the British Deputy High Commission in Kolkata, India can provide consular support to British nationals.
Although there’s no recent history of terrorism in Bhutan, attacks can’t be ruled out. See terrorism
In Bhutan you should take local law and customs seriously. If in doubt, you should take advice from your tour guide. See Local law and customs
Take out comprehensive travel and medical insurance before you travel.