Mathematical Challenges are a series of maths challenges run by Leeds University in the UK. Are questions regarding the rules allowed to be asked in Maths SE?
The United Kingdom Mathematics Trust (which organises these challenges) seems to have a pretty good website, which has information about rules for individual challenges, a good frequently asked questions page, and contact information.
I imagine that going through the UKMT would be a much more effective way of getting your questions about their challenges answered, as opposed to a hodge-podge of users on Mathematics Stack Exchange, including a very large percentage who have never heard of this before, and have no formal connection to it.
I would hazard that questions asked about the rules of these challenges would not be altogether welcome on our site. Our site scope doesn't formally include such "meta-mathematical" concerns.