All the major London airports will use 2.5nm as a minimum separation on final approach when the wx is suitable and there are no wake vortex considerations.
That'll be LL and KK only then will it? SS still use 3 miles as do Luton I believe.
As a tower controller we see the lack of speed control as a real problem. If you are the only Aircraft in the sky, quite often you come over at 7 or 8 miles flying about 200-220 kts ground speed. When radar is challenged they say that there is no need to use speed as this is the only aircraft in the sky. Yes as far as you are concerned it is but what about the departures and my planning etc.
Also pilots not complying. A certain operator is well known for flying at high speed. When you ask the speed they will reply "160 to 4" so I then have to say "what is your speed NOW?" and they still lie (I know because radar have mode s and can tell me). Please make the effort because if you are 3 miles behind a Citation at 115kts and you are at 185kts, there is a good chance that you will go around. So please try and comply and if you are told to reduce to min safe there is a reason why and don't do as a pilot did the other day and still be at 175kts at 2 miles and then get snotty when sent around. I will always try and make it work but we all have to try (that includes you radar!!!
)