Many thanks for your patience. A consumer’s rights in this situation are determined by the Consumer Contracts (Information, Cancellation and Additional Charges) Regulations 2013. These Regulations apply to contracts entered over distance, such as online purchases.
Section 34(9) states the following:
“If (in the case of a sales contract) the value of the goods is diminished by any amount as a result of handling of the goods by the consumer beyond what is necessary to establish the nature, characteristics and functioning of the goods, the trader may recover that amount from the consumer, up to the contract price.”
They may potentially argue that you did not need to remove the protective film to establish that the helmet did not fit properly, although if for example it was the only way to establish the quality of the visor and that is the basis on which you are now returning, then you could use that as a counter-argument.
In any event, they should not dimply reject the return, they can potentially not refund you in full to cover for depreciation in value for now having to sell an item that is not brand new as such, but they will still be able to sell it for a reasonable price so at least a partial refund can still be expected.
Does this answer your query?