Unidentified Ancient Coin?

probably roman emperor Treticus I or II
The head on your coin looks like : http://wildwinds.com/coins/ric/tetr...RIC_0148.jpg
The correct coin can be found on this site : http://wildwinds.com/coins/ric/i.html#T

Very nice Tetricus II imitation, I reckon. Slightly youthful bust, CA at the end of the legend. Could still be a blundered Tetricus I - blundered AVG to GA.

Legend: [? TET]RICVS CA. Presumably standing for Caesar.

Reverse is rotated - if you turn it 90 degrees clockwise, you'll have the correct orientation. I couldnt make much out on it in that picture though.

Kind of. contemporary.

Tribes around the empire, especially during the Gallic Empire (which broke away from the Roman empire, taking Gaul and Britannia with them) which Tetricus ruled, issued their own coinage to make up for the lack of small change. A lot of them issued in such great numbers that you can collect coins from their tribe. I dont recognise the style from UK finds, so id reckon this is from a gallic tribe, but I couldnt be certain.

The barbarous style is due to the inexperienced nature of the die cutters. The coins are also smaller a lot of the time.

EDIT: I looked it up, the CA at the end does indeed indicate Tetricus II, and does mean Caesar and not any other epithet.

Ancient imitations are very neat and aren't 'fake' at all. For .20 that's a pretty cool pick up, and I'd have bought it for an order of magnitude more at least.

Here is a rough overview of some of the terminology around unofficial coins since it can be confusing:

Modern fake, fake: Pretty self explanatory, but a coin that was made in modern times to try and pass off as an ancient coin.

Tourist fake: A coin made in modern times but probably not seriously meant to be passed off as ancient to anyone that is familiar at all with ancient coins.

Replica: A copy of an ancient coin, often not in the correct metal if it is silver or gold, which is stamped "REPLICA" or with an obvious "R" so that it isn't mistaken for the real thing.

Barbarious/ancient imitations: Ancient coins that were made by 'barbarians' that imitated legitimate coins of the time. The style is usually pretty far off, particularly the eyes which they hardly ever got even close to right. I'm not sure if these were intended to be accepted as the 'real' thing or if they were just used for trade among tribes.

Fourees: Ancient coins that imitate (usually very well) legitimate coins, with a bronze or lead core covered in gold or silver. This was done by either counterfeiters or, so I've read, unscrupulous mint-workers who would pocket the difference.

Limes Falsa: A rare type in my experience, but these were semi-official coins minted on the frontiers, particularly when the Empire was in decline and money was short. Sometimes the obverse and reverse are mixed on these.

Value is difficult to pin down. I own quite a few of these which I've cleaned myself. They sell for varying amounts...id value it at about a pound, but sometimes people take a shine to them on ebay and they get a bit higher.