Any suggestions for a tyre for the spare wheel - it needs to be non-directional so it can go on either side.

As long as its the correct size I'd just buy an economy tyre and use as a get you home. Keeping all 4 plus spare in the same wear conditions by rotation is a pain. 4 good ones to drive on, and a cheapie to get you home in case of a flat. FL2 Metropolis, Loire Blue, ebony/ivory

You don't say if it's steel spare or full size. For full size I'd just look out for a second hand wheel with legal tread - after all, you will as like as not never use it, and if you do use it it'll only be a get-you-home expedient. If it's the steel spare, I'd say don't bother and look for a second hand full size! Ex AA Series III LWB Safari - Gone
300TDi Disco (bought new - terrible car) sent back after 18 months
Freelander 1 Estate - leased, given back at end of lease
200TDi Disco (bought from a mate with 100,000 on the clock) - Gone
Disco 2 TD5 - sold and exported to France
FR2 TD4 GS - Gone
FR2 SD4 HSE - Now changed for a DS
New model ex-demo Evoque S 180 in white
Unable to order a new DS, so gave up. Now have a Volvo S90 Recharge.

It is a 2011 SD4 HSE that is new to me (I swapped out my 2008 SE two weeks ago) it has a full size (19") spare however it is a directional tyre (idiot previous owner) which looks like it has never been used.

I may well hang onto the tyre as a spare for the ones on but the spare needs to be non-directional.

I don't think using a directional tyre the wrong way round is a major problem. Assuming you won't be driving it to its limits (?!) it will be fine to get you home - just a bit noisy. and if you need to use it permanently on the "wrong" side you can get a tyre place to switch it round.
I would still look out for a cheap 19" wheel with usable tyre to keep as the spare, then rotate the one you have to get max mileage out of your other tyres. As above, you can always get someone to reverse it for you if need be. Ex AA Series III LWB Safari - Gone
300TDi Disco (bought new - terrible car) sent back after 18 months
Freelander 1 Estate - leased, given back at end of lease
200TDi Disco (bought from a mate with 100,000 on the clock) - Gone
Disco 2 TD5 - sold and exported to France
FR2 TD4 GS - Gone
FR2 SD4 HSE - Now changed for a DS
New model ex-demo Evoque S 180 in white
Unable to order a new DS, so gave up. Now have a Volvo S90 Recharge.

A very well known tyre fitting company once fitted directional tyres the wrong way round on the rear of our old Range Rover. Made the car very light on the back end until I realised what they'd done.