I looked them up on Wikipedia and found they were essentially a stupid design-a heavy tank thought to be needed to mount a big gun when it was found that the Centurion could do the same. They were posted in West Germany for a decade.

But what happened to them? I had thought of various British tanks to use in a Dr. Who UNIT scenario and decided that it would fill the bill, being of the proper era yet not being the latest and greatest, as I assume an organization like UNIT, if they were to obtain armor, would likely to get an obsolete design. If the tank were to be returned to Britain, it would certainly be useful to crush or shoot pesky alien invaders, and have a good chance against their weapons.

I suppose if need be, this could even take place in West Germany.

Hindsight is a wonderful thing, they didn't seem stupid at th time and the threat (percieved) seemed real enough to warrant their construction (The Cent 105 hadn't arrived yet.) Most ended up as hard targets

Unit was supposed to be a world wide organisation under the control of the UN (until they arced up at being associated with SCI-FI!!) They were not of themselves armed with heavy weaponry (except with secret alien technology obtained via Torchwood), but had the ability to call on a parent nation's armed forces for weapons in need - i.e. calling upon the RAF to destroy the Krynoid in 'Seeds of Doom' and the Royal Navy to attack 'The Sea Devils'.

So on that premise, calling upon the British Army for tanks to destroy some menace, and the tanks in question being Conqueror is not outside the realms of keeping within the show's parameters.

As to the Conqueror itself, as a Cold War vehicle, it was not alone in being designed for a role that never eventuated... but what if it did eventuate??? It was supposed to be a long range tank killer to support the lesser armed Centurion.

Of the 185 built around 20 survive in various Museums, private collections and as gate guardians. Not a bad build to surviving ratio considering ….

The Conqueror was designed to counter the Soviet arsenal of heavy tanks and tank destroyers then in the Soviet Army in East Germany; whilst Centurion with a 20 Pdr was deemed to be able to deal with the T54/T55 series (probably just) there was nothing in NATO's armoury to provide a decent enough counter to the heavier stuff, which was also surprisingly agile (just look at any YouTube footage which shows restored JS3s running).

It was a design to provide long range fire to take out the heavily armed vehicles before they could do damage, and remember that there were quite enough to go around equipping Soviet Heavy Independent Tank Battalions. Conqueror had a number of innovations (for British Tanks that is) not least the powerful gun (US design), an optical rangefinder, and automatic shell ejection system (often faulty), and last but not least, a hatch for every crew member. It was reportedly faster across country than the Centurion tanks it was there to support.

Remember that the US deployed the massive M103 for the same reason. Conqueror was of its time and held the ring until the 105mm came into service.

Rob Griffin's excellent book "The Conqueror" lists the fate of all of the known tanks, nearly 150 of them, and as Al identifies, most ended up as hard targets.