Andy gurgled happily, sounding much like they were
saying:

Never understood why they don't just securely lock manhole covers. Yes
I know lost key etc. but it can't be that hard surely?

So there's either a monumentally huge collection of keys, one per
manhole, with an almost 100% guarantee that the bloke who needs to gain
access won't have the right one - or they're all keyed alike, in which
case how long do you think it'd take the scrotes to get a copy?

Always assuming they didn't just use brute force and ignorance to get
round it, of course, thereby hugely increasing the repair costs.

When it comes down to it - all you can do is lock the cover to the frame.
And the frame can always be removed from the tarmac...