THERE IS A LIMITED POT OF MONEY
There really isn't when it comes to benefit claims, being that entitlement is based on need rather than availability.
Again, you've bought the right-wing propaganda hook, line, and sinker if you genuinely believe that's how welfare works.
Love to see your hypothetical UK where there are literally millions of people claiming welfare fraudulently, to the point whereby the country is essentially bankrupt. I mean, you'd think someone would notice all those ESA and JSA claimants suddenly rolling around in Rolls Royces and buying megayachts before it came to that.
If millions of people claim benefits fraudulently, does that affect the welfare budget further down the line? Yes, it does.
Well no, it doesn't, due to this being an utterly absurd hypothetical situation that doesn't resemble reality in any way.
The welfare budget is calculated to include an expected rate of fraud. This has been the way of it for eons, and it has no material impact on successive year-on-year budgets. Incidentally, neither does the enormous amount of unclaimed benefit, which, going by your logic, should apparently result in increased benefits and payments the next year. Except, lo and behold, that doesn't happen either.
You really have no clue what you are talking about. So yes, probably best all around you go to sleep.