Someone I know has just been recently invited to an "assessment centre" on a set date, they were also emailed a link to complete a scenario based assessment . Unless its changed the scenario assessment is you recording your response to a given scenario . My advice would be think before you respond , and take your time , they aren't looking for perfect or for you to respond how a signaller would at this point because that is what training is for , but they are looking for clear communication abilities .
In terms of the interview . In my experience and others I have spoken to it is a fairly relaxed interview . They want to know what you know about the job and network rail as a whole , why you want to be a signaller/work at NWR and then 3 or 4 example based questions to establish if you have some of the transferrable skills form the signalling opportunieis page . Again they are not expecting you to give signalling or even railway examples , but just think of examples of times you have had to remain calm or focussed under pressure , managed difficult situations . If you can then think of examples of times that you have been responsible for the safety of others or had to follow set rules or procedures as these will definitely be strong relatable examples .
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