The Construction Industry Scaffolders Record Scheme (CISRS) appears to be operated by NASC (National Access and Scaffolding Confederation) as their websites shows they both reside at:

4th Floor
12 Bridewell Place
London
EC4V 6AP

CISRS Helpline: 0844 815 7223
Website: www.cisrs.org.uk

NASC's contact page gives its main number 020 7822 7400 which is currently listed as an unverified alternative to the CISRS 0844 helpline number.