Everyone else will be using Trials Tyres as per ACU & MCC Regulations.
Not strictly true. The MCC SSR do allow some non-trials pattern tyres as the extract copied from the 2016 SSR shows below.
'The space between the tread blocks must NOT extend across the complete tyre, measured at right angles to the tyre wall unless broken by a block. In addition competitors in class C ONLY will be permitted to use either Continental TKC 80 tyres or Michelin T63 tyres.'To my eyes, the tyres comply with the SSR because the space between the tread blocks doesn't extend across the complete tyre; they are also described as dual-sport tyres, not enduro tyres. Anyway Brad, the latest update I have had from the organisers is below.
'I am sure we can accommodate both the 15 year old, and his tyres. I will have to check with the ACU about the use of enduro tyres in a trial, as these are prohibited by the ACU but I am told one can apply for a “waiver” to allow such things in a “special” class.'