I can't say with 100% certainty, but found a couple of things which would suggest you will be fine. This is from the website of a Japanese import specialist:

ULEZ Compliant:

Japan Implemented a stricter emission policy before the UK did which means that older cars are subjected to these policies long before their UK equivalents. Between 2005 – 2007, New Long Term Standards were slowly implemented which were then followed by Post New Long Term Standards which were rolled out between 2009-2010. What this means is that most Japanese imported petrol cars are compliant with London’s ULEZ and Low Emission Zones which are in operation in many major UK cities.

And this is from a Toyota UK magazine:

This means that every petrol or petrol-electric hybrid Toyota produced since January 2006 is ULEZ compliant and therefore exempt from paying this surcharge.

From TFL:

If a vehicle is imported from Japan, we would require evidence to confirm it meets the standards. This could be a Certificate of Conformity from the vehicle manufacturer, or a letter from their homologation department.

I am looking at a used Prius import from a garage but it doesn't flag up on any of the .gov or TFL webpages with a validated Euro class status. Does this mean that I will get pinged if I drive into a clean air zone?

I like the look of the car but if it might be an issue for driving into the city'

Thanks in Advance

I think (please correct me if I'm wrong) that cities like London no longer exempt hybrids like the Prius from the Congestion Charge, so really they aren't of much benefit monetarily over newer, highly efficient petrol / petrol hybrid cars, all of which (EU4 and better) are exempt from the ULEZ charge as the Prius is.

Better to go for a newer car, especially one with a full service history (and especially main dealer when in warranty) and nothing serious on the MOT record.

An import per se isn't a bad thing (my now 19yo [EU4] Mazda3 was originally from Cyprus, though I bought it unused when effectively new), but only if you know its history and its proven to be fully UK compliant (mine had a cert of conformity).

I can drive into London with no (hidden) issues - just the Congestion Charge to pay if I ventured into the inner area (which I wouldn't bother with - public transport is still vastly quicker).

If you're in a different region, then check with your local city's ULEZ/LEZ etc to see if there are any variations, thought most seem to use London as the basis for theirs, or are less stringent.

I'd always be wary of 'grey' imports.