My understanding is that in the UK, no reputable agent or publisher would expect payment for submission. Some/many but not all legitimate competitions for first novels and screenplays require payment.
I have no connection with Chicken House though intend entering this year.
Anyone is free to check my posting history and see I've posted about other competitions (off the top of my head, Curtis Brown's, BBC's, Kindle Storyteller, Daily Mail, CWA, Wilbur and Niso Smith...) in the past. I'd not thought about it before but I think all of those were free to enter.
This is a competition that I've posted and I considered it legitimate even though it requires a payment. It is associated with The Times (The London Times for those outside the UK). As a PP have said, this publisher has a legitimate place in the market and is not as far as I can tell a vanity press.
I can see the issue as I think it seems to be Chicken House's main vehicle for submissions too but it is, I understand, primarily a competition with a prize. To be fair to them, most significant UK publishers don't seem to accept unagented submissions at all.
Good luck.