Had a quick glance around at all the usual suspects and a bit underwhelmed with your choices. Especially with the 27.5” wheel requirement. £600 is where your options on 29er really start with the voodoo bizango. Anything with a Suntour coil fork should be avoided as they’re often terrible.
The Vitus Nucleus was the choice before CRC went into meltdown – cane with a 32mm stanchion Suntour air fork.
So personally I’d look secondhand – it’s a buyers market out there so £500 should get you a decent frame / 1x drivetrain / air fork / hydraulic discs / tubeless wheels.
A quick glance at Facebook marketplace and there are loads of Vitus Sentiers about in budget. Some with the marzocchi z2 fork even. Just have to find the 27.5 version (there was also a 29er version) and the right size.
You may find a Sonder Transmitter in budget if you look around.
https://www.facebook.com/share/GRDDbCjeiUtAXFwp/?mibextid=79PoIi
If you’re lucky you might find a Ribble ht725 in budget (or close to it)
https://www.facebook.com/share/aiUBJjLfhQWMiwtE/?mibextid=79PoIi
https://www.facebook.com/share/xWmf7Wq8pw1t7VCh/?mibextid=79PoIi