Here I'm headed to Central London for a day out, just orientating myself.
My usual route is to land at South Bank then walk my way to Trafalgar Square. Then I fly over to Piccadilly Circus, walk from Regent Street to Oxford Circus and then I go along Oxford Street to Tottenham Court Road. Then I go from there to Euston Square. From there, I often fly to the public library near St. Pancras International to have a read and rest.
I've memorised what few no-fly zones there are in Central. These are the royal palaces (including St. James' Palace and Buckingham Palace), Downing Street (where the Prime Minister and other government higher-ups live) and Parliament.
Otherwise, British common law since time immemorial concerning flying species is that if it's legal for you to enter the area on foot without an invite, it's legal to land there if you can do it without endangering people on the ground. This means for example, if you want to land in your back garden, the balcony for your flat or a public square, no-one's stopping you.