Self-tests | Simply Test Me for their day 2 arrival test, LFT @ £12. Much quicker, cheaper and easier than the now gone (for vaccinated people) PCR day 2 test.
It has no bearing on how likely you'll be to catch COVID - the vaccination helps with the severity of the virus rather than whether you can contract it or not. Alas, it could result in more risk as there may be asymptomatic carriers on there who haven't tested because they have no symptoms and they could be easily passing it around without knowing especially if going to the UK as pre-departure tests may not be required depending on the transit point etc.