Originally Posted by 1Aturnleft

Yes BA supports TSA Precheck when departing the US (I assume you're US based.... you haven't mentioned).

If you have a known traveller ID then you can add it to your reservation. Lots of UK passport holders appreciate GE for not having to queue in ridiculously long lines when arriving the US and TSA Precheck is an additional by-product of that. It has no purpose whatsoever arriving, departing or transiting the UK (or any other country for that matter).

Are you on a layover (24+ hours between flights) or in transit (less than 24hrs between flights)? All on one ticket or separate reservations? Detail is important to provide accurate information.

Yes you still need to have your liquids in a zip-lock bag. Individual liquid items still need to be under 100ml per item. Until all UK airports have the new style scanners, the UK stance is all airports follow the more restricted approach in order to avoid confusion.

Originally Posted by pbeee

Airport security in the U.K. is controlled by the Department of Transport, TSA pre check is of no relevance. There is fast track security that is available with business class tickets or for an extra fee but the only difference is a shorter queue.

UK liquid rules can be found here
https://www.gov.uk/hand-luggage-restrictions/liquids

Expect them to be strict to the rules. They are set and policed by the government.

If you are just changing flight then you should be able to check your baggage through to your final destination and do an air side transfer. You will need to go through a security screening to get into the departures area. If you have a longer overnight layover then you will need to collect bags and go through immigration.