TC... from Wigan... yup, it has to be the same TC ! Welcome back! 
I'm on my second Japanese import - my first was a LandRover Discovery V8, and my current one is an 850R, so I can give you some first hand advice 
First off, as mentioned ^^^ the use of road salt in Japan is nigh on non existent, so even my 25 year old 850 has zero rust - this is a pic of one of the sills -
This lack of rust is the primary reason for buying from Japan. However, it does mean that Japanese cars have little rust protection applied at the factory - meaning that you have to have the car treated when you import it, otherwise it'll soon start to show rust spots. I have just had my 850R treated with a mixture of Dinitrol and Raptor paint as a cost of £1300 - that did include stripping the exhaust off, along with the heat shields, arch liners and sill covers etc.
The cars are often low mileage, and with luck you'll find a car with a Japanese service history so that you can verify this. Most if not all cars bought through Japanese auction sites include mileage verification checks.
It is indeed an MoT requirement that the speedo shows the speed in MPH. Older cars like my 850 can have the instrument cluster swapped for a UK spec one (which is what I did). Alternatively you can fit a standalone GPS speedo which displays the speed in MPH - it isn't a requirement that the main cluster displays the speed, just that 'the' speed must be displayed in MPH.. somewhere You might have to have the cluster setting changed to show MPG etc in the computer display - which may be able to be done manually, or may require a dealer computer link to enable - I have no knowledge of the modern stuff sorry 
MoTs are not a problem - mine sailed through without anything needing to be done to allow it to pass any emissions tests etc. The only requirement was the MPH speedo.
A few things to be wary of however...
The export sites/agents use a grading system to identify the state of the car. This grading system is pretty coarse as it is linked into the mileage of the car and its age - so you can't tell whether a car is actually mint but is being downgraded by its age, or whether it has some issues. Just to clarify this with my personal experience, my Discovery had a declared engine issue so was downgraded due to that, however it was otherwise absolutely mint - virtually factory fresh and absolutely stunning. My 850R had a similar grading, however it had no issues but was quite dirty inside and has a few scratches - normally unheard of on a Japanese car.
Taxation class. On both my cars, the taxation class was set as age related, both being pre 2001 cars. The emissions code is declared as 'unknown' - now I don't know whether this is a routine default setting, or whether the DVLA genuinely didn't know and so couldn't assign an emissions code. This MAY have an effect if importing a newer car where taxation is related to emissions - you'll need to investigate that.
Japanese oddities - the obvious one is the radio. In Japan they use a narrower band of frequencies, so you'll need to fit a EU/UK spec radio, otherwise you'll be left with Radio 2 and little else Thats not usually an issue tbh. Japanese tyres are made of a harder compound that EU tyres - they are terrifying in the wet! So you should assume that you'll need a set of tyres asap The heat in Japan can cause all sorts of issues with plastics and rubber. The plastics become brittle, and the black sealant often used around windows degrades causing nasty black streaks when you wash the car. If the car was parked under a sunshade/car port (as is often the case) then you might see the front / rear plastics being different shades due to sun bleaching. You'll often find the leather is hard - it'll need a thorough clean and conditioning to bring it back. Finally, the Japanese LOVE their electronic gadgets, so be prepared for a lot of superfluous wiring. If you're lucky it'll just be a toll card transceiver, otherwise you may have aftermarket TV/DVD players, media players, and other devices which can't be readily identified My Discovery was white with blacked out rear windows and a pair of twin telescopic antenna on the roof - they were for a TV/DVD system, but many UK drivers assumed it to be a Police car which was hilarious on the motorways
Finally, you'll have to assume that a Japanese car is just the same as any other used car - the suspension, brakes, etc etc will need to be checked and the usual 'stage 0' maintenance work undertaken.
IMHO its definitely worth buying a Japanese import - the ability to simply unbolt stuff without anything snapping is priceless You'll be amazed at the condition of these cars - the Japanese MoT (the 'Shaken') is very expensive and very thorough, so keeping cars on the road out there is expensive and they take great pride in them. Plus their national mindset is one of mutual respect, so they tend to have very little damage - even cosmetic blemishes are attended to.
HTH
Edit - insurance. Forgot to mention this sorry. A lot of the mainstream insurers do not like imported cars and will not quote on them - something that surprised me as my Japanese spec 850R is virtually identical to the UK spec one (with minor technical differences). However, the usual specialist insurers are happy to provide competitive quotes, so it isn't really an issue - unless you are going for something genuinely JDM (ie no equivalent UK/EU model such as the S-Cargo and Cappuccino).
