Sadly you will not be able to make the fitter do anything - this would most likely be the outcome also if you went through the courts as well.
You are getting a lot of disinformation in this thread from some people who sound like experts in their field. Sid Bourne mentioned is one of the foremost technical experts in the country however I am unsure if he has owned both a commercial and retail enterprise - I do.
I have run our family business which is 126 years old for 23 years. This in itself means nothing as I have met many people in my industry who have worked in it for decades and they still don't know what they are talking about!
I would put myself forward as exceptionally competent in technical issues although I don't claim to know everything - I do know who to ask if I am less than 100% sure about anything and I have done this thousands of times over the years - this has made me correct on most occasions which is mostly down to who I know not what I know.
The following information is based discussions with the Contract Flooring Association, Citizens Advice and company Lawyer
1 - Buying product as supply only then organising the fitting yourself - this could be argued that you are undertaking the role of main contractor and as such responsible for ensuring checks are made lie with you.
2 - Buying product and services from a retailer - no matter if a retailer had you sign a disclaimer to absolve them of responsibility should something go wrong like your experience - this would mean nothing - as a consumer you are deemed not expert and the retailer as the main contractor in this instance is responsible for testing to ensure the subfloor is fit for purpose - your floor was not
3 - If flooring is installed by a commercial flooring company through a main contractor e.g. you buy a new house and the builder has the floor fitted by a flooring company - This would be challenging but legally the main contractor is responsible for handing the building i.e. the sub floor over to the flooring contractor fit for purpose (we always take moisture readings as building contractors have no clue how long it takes for screed slabs to dry)
I am unsure if you will have a claim but I would suggest contacting your buildings insurer (carpet claims would be contents - hard flooring is always buildings insurance)
Lastly, as a long established business who 8 years ago was selling over £250,000 worth of Amtico per year, my company has taken the commercial decision to step back from LVT (plastic tiles).
This is the fasting growing market which means more and more people want them.
This also means
1 - China is flooding the market with cheap options which in the same way as laminate flooring became a bad word, LVT will soon be thought of as being rubbish (not true for quality LVT or Laminate)
2 - As it appears to be very expensive to lay - a £35 per square meter product can easily cost £75 per square meter or more once installed - many people go down the route of buying it online or through a fitter and then organise fitting themselves - often a big mistake
A couple of thoughts to finish
1 - I'm not bitter about LVT - I sell loads of it cheap through my cash & carry business which is separate to our high end retail business - I am just not willing to offer our considerable expertise for nothing.
2 - other parents - instead of LVT check out Berry Alloc High Pressure Laminate - this is the only laminate made the same way as Pergo used to be. Pergo was the product that started the Laminate flooring revolution and everyone wanted as it was brilliant (the new Pergo is not HPL and nowhere near as good). We are still replacing Pergo floors that look brand new after 20 years because people want a change. Berry Alloc may cost you £35 - £45 per square meter however it will only cost £15 - £20 per square meter - zero moisture issues as well as it is laid in a different way.
I hope you have managed to stay awake to the end of this 😊