In reply to muppetfilter:
No, I am aware of it, I just don't believe that handling something that has been outside would class as a substance hazardous to health, nor apparently is it something the very anal auditor who likes to pick apart my work thinks either as mud and dirt is something that workers at the place I do health and safety for do come into contact with. I did however get in trouble at my last audit a month ago for failing to assess and document some old tipex he found in a drawer that I didn't know was there, because that actually is covered by COSHH.
But that's not really my point, my point is that the law does not forbid people from handling muddy boots.
If their reasoning is health and safety then the correct phrasing should be "due to our interpretation of health and safety regulations..." Of course most things with H&S law is down to interpretation, but in answer to the OP's question about whether or not the law forbids you from touching dirty shoes, the answer is no.
I imagine people working in shops come in contact with all manner of diseases, as do the rest of us, and a pair of boots is unlikely to be the cause of the issue, especially as if it's dirty people probably aren't going to touch it anyway, certainly not smear it all over their hands then lick their fingers.
And one pair of boots is less likely to be harbouring anything particularly nasty than every other pair of shoes walking in and out the shop, spreading their deadly poison. Or on the hands of customers, pawing everything. I imagine the shop is already crawling with enough bacteria that being worried about a single pair of shoes is worrying about a drop in the ocean.
On a related but unrelated note one first aid trainer I had said you're most likely to get Weils drinking from a bottle at the pub, as they've been pee'd over by rats, I always wanted to find out if it was true.