Ring and explain that tubeless tyres are 1) a selling point, and 2) considered more valuable that the tyres supplied.
Your deal is with the point of sale at the moment, for the first 12 months of warranty, and time given for distance selling regulations (if you got it mail order) and any other regulations on their website you ordered through.
I note in the Terms and Conditions they state:
“This site is provided on an “”as is”” and “”as available”” basis. No representations or warranties of any kind are made, express or implied, as to the operation of this site or the information, content, materials, or products included on this site. You expressly agree that your use of this site is at your sole risk.”
This is horrifying to me. Using the site at “my” risk? Not their’s, under UK laws?
Must be why they think that you are responsible for any COSHH issues with returning the “goos” to them.