GUEST,Mr Red

Maybe I should leave well enough alone, but Guest Mr. Red, I didn't get your punch line.

You wrote:

"I have a collection of 4 leaf clovers - so where is my winning lottery ticket? I know, I know. Still in my pocket, it's round, metallic and it's number is 1 GBP."

So my question to you is what is the significance of "1 GBP?"
Is this an UK thing? Is it like an army ID tag?

I hate it when I don't get a joke because I can't understand the punch line.