Next time you're down at LGW, look at all the buildings above the South Terminal, Concorde House etc. There'll all built just under the transitional slopes and if you're far enough back (say about the Fire Station) you can draw a nice imaginary line which conforms to the transition. The South Roof Office block is 9 floors -if you look at the EGKK Aerodrome Chart in the UK AIP there's an obstruction light on it quoted as being 120' or about 37 metres above the ARP. Unfortunately the pictures I have illustrating the ST aren't in a format that can be shown on pprune - be much easier if we could insert jpegs!
The hangars on the South Side are also just scraping the underside of the surfaces, such that if they put scaffolding up for repairs it sticks up into the side slope and has to be NOTAM'd as an obstruction.
There's a great illustration of all the surfaces in CAP 168 Chaper 4 page 10 fig 4.11
CAP 168 conforms quite closely with Annex 14, it's just a bit jumbled up and difficult to reference sometimes. The CAA have had several goes at re-writing it but in my opinion it needs a fresh mind to come in and start with a blank piece of paper rather than just updating what's there. No, I don't want the job!!!
Cheers,
The Odd One