I don't think the squeezed middle has anything to do with income. It has to do with what is seen as "middle class".
It then depends on what you view as a "Middle Class" lifestyle.
I probably had what I consider to be a very (upper) middle class lifestyle:
We had 4-5 week summer holidays in either Europe or far-flung places (U.S., Australia, Africa, Asia…). When we stayed in hotels, it wasn't uncommon for us to stay in suites. I can only recall ONE summer holiday where we stayed in the country. I did horseback riding and so did a lot of my friends. Others around me would play tennis, etc. Most families around us could buy gadgets, etc. without having to think about buying them. My dad bought new cars - one for him, one for my mum. Mum was a SAHM. Dad had a very stable job. My brother went to private school for a while, I went to grammar.
My DH and I have a current household income of over £100k. We have a very small household, and know we'd need to earn more, if we wanted to have two DCs (nursery fees x 2 = min. £2k per month). There is no way we can afford the life I had when I was a child, but that is the life I normally associate with being 'middle class'. To have that sort of lifestyle, I think we'd need a combined income of over £300k. Hopefully, one day, we will get there. But it feels weird doing essentially similar jobs to your parents (both of us), and not have the same life you had whilst growing up. Because of that, it does feel like you're 'squeezed'.
Now, I know that there are plenty of people earning less in the UK. But to afford the "middle class" lifestyle, you do need a lot more money these days than what middle class jobs can offer. It's not about being on the breadline. It's about not being able to afford what you EXPECT to be able to afford, because you're essentially doing the same job as your parents (in fact, double so as there's no SAHP. That is the essence of being squeezed.