Normally bad form, but like you say there may be exceptional circumstances.

I was going to ask "Do the ones at LHR not require RADAR keys or similar to stop misuse?"...

Then I thought I'd do more research on Google to find out more about the scheme, is it a worldwide scheme so would be suitable for international airports or UK only so not really suitable.

Searching Google for 'RADAR key' has Amazon in the first ad spot linking to sellers that are selling these on for just a few quid.

If they can be picked up this easily the scheme loses most of its point and shame on Amazon for promoting this practice by paying for Google ads.

Basically if they can get these keys for a few quid it means that those who have no issues using facilities can gain access, but anyone who'd normally never think of using them and has exceptional circumstances can't gain entry.