Come on someone had to suggest it.
OK. So I think that we are going to go with a few of the suggestions above. Not the dynamite or cat pee though - SWMBO is quite strict about the use of both.
I the first instance I like the idea of heating the concrete up to get it over with and I can see that having some effect - it certainly won’t cause a problem if we end up going down another route. We can also do the PVA test at the same time to see if we can seal it in that way - part of me really likes this approach as we can water down the PVA so that it flows into any hard to reach nooks and crannies - I realise that it would mean multiple applications though. If the PVA doesn’t work then lemon juice can be applied. Failing all of those then dynamite it is - I draw the line at cat pee.
Ha! We found a new leak - very small, but a leak anyway. With diesel a little oil goes a long way for smell. Anyway, fingers crossed it has sorted it out. We have used kitty litter and a couple of bowls - one of vinegar and the other with diced onions to absorb the smell and are hoping that it is the end of the saga for now - we will be heating the concrete up under the boiler in a week or so.
Thanks for the suggestions - they are much appreciated.