Flying Lawyer, you said:
Twin-engine helicopters are not restricted to the Heli Routes and the clearance will be "not above .......... feet."
Correct,
but only in CTR West or CTR East. CTR West is west of the line from Denham to Brooklands, and CTR East is eat of the lines from BNN 143 - EGLW - Due South. Here twins can fly off the routes. (Hence departing EGLW Brent or due South LEVEL at 1500 as all flights in the segment of 020 - 140 degress based on EGLL must be level at 1500')
In CTR Central (the bit between!) they must fly on the routes unless of course they are on a LL Ops approved Non Standard Flight "Whiskey" number!
Crossing LL is hard work and you need to know the rules but is very rewarding. Managed to get a pic of an AFR 737 flareing below us!
Otherwise all spot on - and us overworked underpaid staff on 119.9 and 132.7 are always available as ballast on trips on the routes!!!
Cheers