What happens it somebody steals your tax disk whilst your away from your bike and then a Policeman sticks are ticket on it for non display of a tax disk before you get back to it?

This has happened to me with a loan bike (no fine) when mine was in for a service.

Do you think it would be acceptable to the Police if I was to photocopy the tax disk and display the copy on the bike but have the real one in my wallet should the Police wish to see it?

I called DVLA but they said it would be a matter for the Police as they enforce the rules