I don't know if there is an official join point on downwind but I would aggree with the other pilot "join at an extended west downwind position, that way you would not be in a head on conflict with circuit traffic. (Noise abatement permitting)
If your instruction from ATC was (report) downwind, I don't think that means (join) at that point, rather "report once you are established there".
Perhaps an expert will put me right, but we have a similar circuit pattern, north of Edinburgh accepting similar directions of joining to 25/07.
Trevor.