I fitted an electric block pre-heater yesterday a German brand called "Hot Frog". The model that arrived was a bit oversized for the car. I ended up squeezing it in in the by-pass hose between the cylinder outlet and the heat.
When I tested it rasised the coolant temperature from 3.5c to 21c in less than 10 minutes after that rate of warming up slowed down and peaked at about 55c after 30 minutes. On start up the upstream oxygen sensor came to life almost immediately and the engine went closed loop in just over a minute.

I've often thought about one of these. It could save a life t of wear. Does it pump oil or water around?

Still growing palm trees down south, no need for that malarkey

Have thought about fitting one of those to the TVR.

Speed 6 is very intolerant of not being properly warmed up before opening the taps, but it can take 5 miles or so to warm up.

Do you have any more details ?

https://shop.strato.de/WebRoot/Store10/Shops/10116541/4E8D/AA6F/FEF8/BC25/ED35/C0A8/2935/B00A/assembly_UK.pdf
https://shop.strato.de/epages/10116541.sf/en_GB/?ObjectPath=/Shops/10116541/Products/0080P

If you do an search engine pre-heater or coolant pre-heater on ebay you should find a selection mostly from Germany and eastern Europe. I got the 2200 watt Hot Frog but it is a bit on the big side, the smaller black version is 1100 watt it has the inlet and outlet pipes better orientated for easy fitting.
It is also sold branded OWL-2 or SKU-2 or ATO-1.

I have a diesel fuelled unit from a Saab fitted to my ambulance wired on a timer. It really needs a circulation pump but it drags the temp up from 5* to 20* in about 10 minutes and that gets the coolant circulating using rising heat. Then it soon gets up to 40* which is where the stat shuts it off. It's lovely to have a warm heater and defrosted windows on a winters morning.

I have the Kenlowe electric preheater set-up, for sale, in superb demonstrable health.
Used briefly when I had a momentary lapse of reason (it's an age thing) and ran a Vauxhall XE race car, requiring such care. I'm now back to small bike engines...