Spiral,
I've been retired a while, but a good initial source of information is CAP 493, (available online), which is The Manual Of Air Traffic Services Part 1. Its contents apply to all U.K. ATC units and Section 5 deals with emergency situations.
Each unit also has a 'MATS Part 2', which covers the procedures at individual ATC units, but these are not usually available online.
I dare say lots of information will follow from those currently working at ATC units or in the training system.
Also, certain NATS units often ask for aircrew to take part in 'emergency training days', often at the 2 main ATC centres, but it's always worth checking with aerodrome units too.