4" front door, rear door and rear pillar.

You can fit 5" with a bit of fettling.

 

 

 

KEF are as British as it gets for speakers and are still manufactured in the UK

Head unit is a no go as everything electrical/electronic is made in China

But if you want a good one then I recommend a Sony DSX-A300DAB, I recently bought one as it is without CD and it was extra short to fit better in my 200Tdi Disco, it's DAB, Bluetooth and aux compatible and has all the connections for a hard wired amp & sub.

 

 

Morel used to be made in England and really good speakers-used to buy these from"Parts Express"back in the '90s and'00s Just checked and PartsExpress still has this brand but they are now marked "made in Israel"...possibly with British parts.I have a couple morel woofers bought~Y2K that will find their way into my'03 D2 The original speakers in the D2 are made in Belgium by Philips.Dynaudio-Made in Denmark-are really good! expensive,some Volvos use this brand and wrecked Volvos might be a good source of some really good speakers

 

Back in the 1980's I had a pair of B&W car speakers in one of my cars. They were incredible but I seem to recall they were madly inefficient. As a result, I had to power them with about 100 watts (I know that doesn't sound like a lot these days) a piece to get them to perform. Does Meridian still make car audio equipment? Maybe they might offer an alternative to KEF.

And if you want the ultimate in British electronics, look into Naim Audio. I had a bi amped Naim system for my home for years back in the '80;s and '90's. I think they do all the Bentley audio systems.