James,
Try NATS Swanwick as i also said to you on MSN. I almost got a placement there but told me applications ended December time for your year Group 10.
NATS careers
I seriously would not bother with Heathrow and BAA as i had huge problems with them, not worth the 4 months and a waste of time and they Say NO because of Duty Free stuff like Alchol and then another excuse Security pass was needed that takes 6 months according to them what is more appropriate than because there is Alcohol on the Airport site and underage stuff.
Tell them your looking for work experience at Swanwick and your very interested in becoming a pilot and make sure you read it over before you send to them.
Also Heathrow Tower and Gatwick Tower are both Airside and the likely chance of anyone not working there getting there hands on the Door handle are remote.
Regards,
Robbie