I have flown this route many, many times in the Aztec (in the days when I was at Fairoaks) and know it like the back of my hand.
As AlanM (no relation to the Fairoaks AlanM, I trust?) says, it is important to understand the clearance and follow it. He says that BUR is easier to find than Ascot and if you have ADF or GPS this is true. However, I don't believe that either bit of kit is a requirement for SVFR, so I will describe BUR for the VFR pilot.
As you leave Ascot the track is (near as dammit) due North. The distance is very short, so provided you make a sensible correction for wind there should be no problem getting very close to BUR. You are low, so picking out landmarks can be a bit dodgy (especially as this area is a wasteland of big houses with swimming pools) but you should be able to see Windsor Castle to your NE. Stay well the the West of that, and you will see two towns (Slough and Maidenhead). Aim to keep them either side of the nose, aiming for the gap between them. BUR itself is right next to a supermarket in among some rivers and ponds.
It may also be useful to know that Ascot stands out as a large low white rectangle, easily visible from the Fairoaks overhead.
On the subject of the BUR Ascot corridor, if you are using it to go South from the Midlands you may well be given a clearance to enter the zone not above 1500', to be below 1000' at BUR. You have to very careful not to get too low coming over the Chilterns, I would suggest not descending below 2000' until abeam High Wycombe/Amersham, then descending quite sharply (in a fast aircraft) to 1500' before the motorway then continue the descent to 1000'.
The SVFR controllers are much happier to give you a climb going North (often to 2400' as you pass BUR), so terrain clearance isn't usually as much of an issue in that direction, but if they give you 1500' to the zone boundary, be ready to climb as soon as you see the motorway. Also, don't blunder through the Booker ATZ.
May I make a plea for everyone's sake? The Thames/SVFR guys are a great bunch, and they make Ascot-BUR as available as they can, but they are increasing their already considerable workload, because they have to watch us like hawks as we go under the jumbos, to check both our position and altitude.
Nice as these chaps and chappesses are, I am quite sure that if enough plonkers who cannot hold heading or height use the route, they will have to reduce its availability. So Please only use it if you know what you are doing...for all our sakes!
W