I’d say it’s a bit of a grey area, as if you’ve been offered a job pending medical (and most pass the medical), you’re technically a driver and so the psychometric assessments may not be considered. That’s not to say I’d want to risk it

.
Also, I believe when you apply for your ETDL (for me it was about halfway through classroom training this was applied for, I assume so you don’t have to wait once qualified for a licence) the psychometric assessment passes are checked by the ORR, so if one did slip through the net, it would probably be picked up at this stage and bounced back to the TOC/FOC (it’s very easy to dismiss someone if they’ve been at an organisation for under 2 years too…).
It’s a position I found myself in when I went to GWR. My psychometric passes were dotted about everywhere, and SWR would only accept passes for 3 years. I decided not to take what I needed to again with them, even though it was easier if I got the job to stay at the same TOC, because if I failed, I’d be back to square one (GWR accept the passes for 5 years so I was straight to interview with them).