In a significant change to the UK’s rules, passengers connecting airside at Heathrow (or any English airport for that matter) now need a negative COVID test before departure, in the order to Transit. Previously airside passengers did not need a test to transit. The rules are here. A passenger locator form is no longer needed the web site says, although one was processed when I transited about 10 days ago.

Passengers doing a land side transit, where they enter England need to follow most of the rules as if arriving in to England. This is what you need to do:

You need to take a COVID-19 test before you travel to England.

You must complete a passenger locator form before you travel to England.

You need to do the following when you complete your passenger locator form.

• select ‘Stay in the UK’ under the Your travel plans section
• reply ‘I will be travelling for an exempt reason’ to the question about whether you are required to self-isolate on arrival
• select the Exemption options, and then select ‘Transit Exemption’

This includes if you are transiting onto the Channel Islands or the Isle of Man. You may need to show evidence of onward travel and where you will be staying at the border.

When you are in England you do not need to quarantine or take any COVID-19 travel tests.

You must either:

• remain within your port of entry until your departure from England
• travel directly from your port of entry to another port of departure in England

Full details, including travel requirements for the Common Travel Area are to be found here.