As other have stated you need to get a designer to inspect the scaffold and report if it is adequate to the old BS5973 when it was first erected and any changes which are needed to comply with TG20:08.
If you have the original enquiry and order from the client which states the hire period then additional strengthening may have been needed as the scaffold goes from a temporary structure loads to permanent if it is there for longer than 2 years.
Think they are trying it on if they are claiming back the extra hire. Client bully boy tactics. You need a good legal surveyor to argue that one.
If you got any photos or other info then happy to look at for you.
See you in Bournemouth, I am local lad in Christchurch
