70-75 in a 50 on the motorway will be a fixed penalty mate, 3 points and £60 fine.
You can contest it in court if you want, there has been a lot of ways suggested to get off with been caught by a speed camera. tbh not many work, if you contest it, and they've got photographic evidance to prove it was you then they'll shaft you!
Best to take the 3 points, insurance dont even bother about the first 3 points so your not losing owt other than the £60 fixed penalty.
You might even get away with it, if the brown envelope doesn't turn up on your doormat in the next 10 days you'll be fine.