Morally it's wrong. That said you almost certainly won't get court, a university which deals with thousands of applications is not going to call up the library/soup kitchen/charity shop to see if everyones story checks out.
If you have an interview I doubt they'd spend any time talking about it, its irrelevant to the degree.
But lets be honest, is it going to make any difference if you volunteered in a library? Absolutely not.
The top unis like Oxbridge/LSE care pretty much exclusively about academia,
and with the rest of the universities it's more or less the case that as long as you have the predicted grades in good subjects you will receive an offer.