Hi Ash.
Firstly, your 'gesture' was exactly that. You made it clear there was no liability taken. The law does not see that kind of thing as normal people see it. The law sees that gesture as simply that NO inference whatsoever. That is now concluded.
However, it works in your favour as you have demonstrated you wished to move towards them. She has remained intransigent.
You have also asked for further information, disclosure in legal terms. They have either ignored or refused to supply that information. The court will require it believe me.
If it were me, I would not even acknowledge the requests. Why? To do so puts her in charge, leaves her to drive it and you to respond. Personally, I would resend the letter asking for full disclosure and breakdowns of all costs but now it would be minus the gesture. Perhaps. and I am not certain here so you need to take some advice, you now start talking of your accrued costs.
When she issues the court order, you have the chance to issue a counterclaim. Another alternative is to issue a court order against her before she raises one to you for the harassment. Again advice reqd.
The bad news there though is that as a self employed person, where we all minimise our tax liability and therefore minimise our income, your potential claim will be quite light in terms of hourly rate. You can completely forget £400 a day unless you can prove you are currently paying tax at that same rate.
As already discussed however, and hopefully you've carried out, you'll have kept contemporaneos notes to indicate just what time you have spent defending yourself against this daft accusation and therefore be able to quantify time spent.
The reality of these cases is that often, even if you win, the judge may tell you you have nothing to claim. You will have 'won' in the eyes of the law but it will have cost you to do so. It may well prove more expensive to defend your honour than to roll over.
In order to minimise your costs, I would draw up a summary/timeline of events to take to someone so they can get stuck into it without racking up too many hours at £200 per hour.
Or just meet her in dark alley and graphically explain her future to her 😱 JUST KIDDIN!
PS. What you can do in the meantime is to gather evidence from an independent engineer (e.g. someone who's perhaps a CIPHE member) who will act as an expert witness on your behalf. The cost of this will form part of your counterclaim. I would be asking what custom & practise is (so what normal plumbers do) for the scenario you encountered. Personally I know of no one who would have checked for pipes underfloor. It is not 'reasonable' (legal term for normal) to do so. Even if they say it is one can soon inject an element of farce into what might be a problem. Most of the time you can also through their desire to keep costs down back at them in those circumstances too so you were forced by the insistence to keep costs down to do a minimal job. You get my drift. In court they'll look bloody daft.