We all seem happy about the extra mile behind a 757 on approach, but the main thrust of this thread is departure separation timing.
Every ATC provider has their own minima. Couple that with differing company minima and we've got confusion. Confusion must be avoided and this should be done by deciding whether or not a 1 minute separation following a 757 on departure is appropriate or not. Either way, once a decision is made we will all be singing from the same hymnsheet.
Until that decision is made, if you're in the UK (where 1 minute separation is approved for ATC) and you're behind a 757 in the queue and you want/need 2 minutes separation, please inform ATC prior to line up. You never know you may just depart first!