Most visits to the UK are trouble-free but you should be aware of the global risk of indiscriminate international terrorist attacks, which could be against civilian targets, including places frequented by foreigners.
This advice is correct at time of publishing. As the situation can change rapidly, visitors are advised to contact the following organisations for the latest travel advice:

US Department of State
Website: http://travel.state.gov/travel

The Ministry of Foreign Affairs in your home country.

Inbound flights to the UK from Turkey, Lebanon, Jordan, Egypt, Tunisia, and Saudi Arabia are subject to additional hand luggage restrictions, imposed from 7am on Saturday 25 March 2017. All phones, tablets or laptops are banned from carry-on luggage and must be placed in hold luggage if they are larger than:

● 16cm in length.
● 9.3cm in width .
● 1.5cm in depth (thickness).

The UK Foreign Office advises travellers contact their airline before travelling to find out if they will allow specific electronic devices or electrical items on the flight.