A few issues to work on..

[David]

I've done the 'demist' test and the radiator fan does not spin up. It does come on when it's hot though, but I'm guessing one of the speeds is broken?

Probably the fan resistor needs replacing.
https://www.dmgrs.co.uk/products/rov...airs-pgj000110
Bumper-off job, but easy enough to do as a DIY task.
http://www.spunagain.co.uk/ZT260fan.html

Coolant leak from the manifold and the last few days I've been having rough running issues.

Probably coolant in the plug well recess(es). Detach a coil from some of the plugs in the area of the leak and see (single special locating bolt, 7mm I think; careful not to drop it). No need to detach the electrical connector on the COP to be able to pull it off the sparkplug and out enough to look. Probably soaking wet. If you have a OBD-II tester, you will probably see P-codes pending, showing precisely which plug(s) are misfiring.
If so, look towards fixing/replacing the leaking manifold ASAP, otherwise the long springs in the coil-tubes which connect to the plug-caps, will start to rust, necessitating replacement of the COP. Anyway a leaking manifold will only get worse, whether it be a gasket or "plastic rot"

David

[Gaz]

Probably the fan resistor needs replacing.
https://www.dmgrs.co.uk/products/rov...airs-pgj000110
Bumper-off job, but easy enough to do as a DIY task.
http://www.spunagain.co.uk/ZT260fan.html

Probably coolant in the plug well recess(es). Detach a coil from some of the plugs in the area of the leak and see (single special locating bolt, 7mm I think; careful not to drop it). No need to detach the electrical connector on the COP to be able to pull it off the sparkplug and out enough to look. Probably soaking wet. If you have a OBD-II tester, you will probably see P-codes pending, showing precisely which plug(s) are misfiring.
If so, look towards fixing/replacing the leaking manifold ASAP, otherwise the long springs in the coil-tubes which connect to the plug-caps, will start to rust, necessitating replacement of the COP. Anyway a leaking manifold will only get worse, whether it be a gasket or "plastic rot"

David

Cheers! . Is the gasket easy enough to replace? And where to buy in the UK?

Also where best to get a manifold in the UK if its cracked/no good?

Side question about the manifold, does coolant only flow though the separate pipe on the front of the manifold?

If it does, I'm curious why they bothered sandwiching the plastic manifold between it and the head? And not directly to it.

But I'm probably missing something in the design.

[David]

... But I'm probably missing something in the design.

Yes I think you are!

Getting a new manifold in the UK is virtually impossible. Stateside, and then only original Ford Performance, M-9424-P46, not Dorman (Amazon/RockAuto etc.), if you are sensible. Get the gaskets at the same time. Manifolds are difficult/impossible to repair, and second-hand ones are very rare, and generally not to be recommended.

Just the gaskets from Brown & Gammons at https://www.ukmgparts.com/product/r7...each-lkj000080 , or DMGRS at https://www.dmgrs.co.uk/products/mg-...anks-lkj000080

... more important though is to get your full membership sorted out, since I just noticed you still haven't done that, and not being "green", will be unable to read most of the vast amount of advice here you obviously need, in threads which are closed to you. Same applies to your questions in post #11, I'm afraid.
My £50 MGOC renewal just plopped through the letter box, obviously far from welcome, but worth every penny for the full Two-Sixties access.

David