Please don't phone us and ask to route over LHR!
It is not easy controlling when having a laughing fit.
The ASCOT BUR route MUST be flown not above 1000'. Please make sure you get your NAV right. As FFF says, you will get barked a if it goes wrong, and if you suddenly turn towards LHR and departures stop launching outbounds it will inevitably mean a lot of paperwork and a probable court appearance!
HOWEVER! - don't let that scare you. It is easy to fly - Ascot racecourse is very prominent with it's grandstands, and obviously BUR is a doddle! You might get BUR direct to Denham and derestricted up to 2000 feet - but don't forget that Denham may want you to enter via the correct lanes. If so - pleae turn away from LHR!!!
When coming from the south east I often offer via the Fairoaks overhead to Ascot level at 1500' and not above 1000' on crossing the M3. YOU WILL BE SENT TO FAIROAKS on 123.42 for YOU to request clearance through the ATZ. IF you don't get it, again, don't turn towards LHR in the zone!
How much time does it actually save though?? Is it really worth it as you can stay outside and be up at 2400 feet.
MY personal advice, is to do it for the first time from the north. It is much easier to find BUR than ASCOT if you are not familiar. You also need to avoid the danger areas at Bagshot and of course the Fairoaks ATZ.