I was under the impression the departures from 08 turned left/right before Stevenage. However there seemed to be quite a few departures yesterday morning (Sunday 21st) that all but continued on the runway heading (especially the Wizz flights). Is it simply the case that traffic was such that they could be routed that way or has there been a change to the SID?
You are correct, none of the Luton 08 SIDs involve maintaining runway heading beyond the LUT NDB.
Of course ATC have the discretion to send aircraft off-track to avoid weather - could that have been an issue yesterday morning ?