Hi Javelin, surprised no one has answered you yet.
As a lowly operational Atco (Gatwick Approach), I have no knowledge of this procedure (although that doesn't mean your guys haven't passed it to our guys).
At Gatwick I would be surprised at your early turn back to the field. Experience shows most engine failures on departure would climb straight ahead unless the aircraft was on fire.
The problems your turn would cause would primarily be with the next departures, hopefully the tower controller would be aware of your problem and not launch anything behind.
Bottom line is though, if you're having an emergency we should expect anything.
If you find yourself in this position squwaking 7700 would get everyones attention and get a PAN/MAYDAY call on the tower frequency if you have time.
Are you going to tell us which airline?