The £10k question.

I would throw it at my current car probably, or a Golf GTi or a Skoda Superb.

Or £1000 after paying for a year's road tax.

www.autotrader.co.uk/classified/advert/201908030749815?atmobcid=soc3


Under budget. 30 quid a year road tax. 45 to 55mpg. Loads of room. Remappable to around 235bhp. JD.

I like your thinking!

Lots of space in this

www.carandclassic.co.uk/car/C1155199

Gosh!

www.carandclassic.co.uk/car/C1170522

Surprisingly slim pickings at £10k

My initial go to would have been an early F10 5 series with the 3.0 petrol six (a 523i or a 528i), but I could only find one car under £10k

The Merc is lovely but I suspect it would drop you in the clarts financially with very little effort.

The 4.2 engines in the XF are the more robust of the V8s (Jag or otherwise) and aside from the touch screen graphics, have aged well and are still very pleasant to drive. So that is where I would be sticking my £10k

First thoughts, looking on the "only car and it must be practical" side:
www.autotrader.co.uk/classified/advert/201911074110414?advertising-location=at_cars&postcode=rg224bs&keywords=scout&body-type=Estate&make=SKODA&sort=relevance&price-to=10000&onesearchad=New&onesearchad=Nearly%20New&onesearchad=Used&radius=1501&price-from=9000&transmission=Automatic&page=1&modal=photos

... except that looking at the fit of the headlamps, it appears to have had some sort of accident in the past

... or
www.autotrader.co.uk/classified/advert/201909122158933?price-from=9500&price-to=10000&make=AUDI&sort=relevance&advertising-location=at_cars&radius=1500&postcode=rg224bg&onesearchad=Used&onesearchad=Nearly%20New&onesearchad=New&model=Q7&page=1

or
www.autotrader.co.uk/classified/advert/201903165949367?price-to=10000&radius=1500&onesearchad=Used&onesearchad=Nearly%20New&onesearchad=New&make=VOLVO&price-from=9500&sort=relevance&postcode=rg224bg&advertising-location=at_cars&model=XC60&page=1

This looks good, ex-Sir Andrew Lloyd-Webber apparently:

www.autotrader.co.uk/classified/advert/201907039681144?advertising-location=at_cars&price-to=10000&postcode=rg224bg&make=MERCEDES-BENZ&price-from=9500&sort=relevance&radius=1500&onesearchad=Used&onesearchad=Nearly%20New&onesearchad=New&model=S%20CLASS&page=1

Possibly not the best colour choice, but I don't find it objectionable.
It looks to be a lot of car for the money

.

330d Touring or the best diesel Superb estate I could find.

Or, buy a South African import Mk2 Escort and a basket case 850 T5 and combine the oily bits.

I'd only want the engine out of one.