That's what I was fearing, but I still work in the same building with the same brand name, doing the same job so I still worked for that company brand name but it's owned by a new company. On the website is has the brand name everywhere, but in small print on he page where it says shworooms are it says the 'brand name' is a division of the 'new company name'. Going by how the CEO of the new company is, I'm pretty sure that they will try and get away with paying us the minimum and all my 18 1/2 years will mean nothing. So they can really wipe of 15 years service and you get nothing for that from anyone?
It is a good idea to consult a solicitor. One that specialises in Employment Law. Most will give you some free time upfront. You can slip in a few questions and they will often answer them. I managed to get a good 45 minutes with one but had no need to use one in the end. But I managed to find out quite a lot as a result, where I stood etc etc

I have never been a member of a Trade Union so can't help you there.