Old Roman Or Greek Coin I Need Help

I'll have to agree with SAP; it looks a little 'iffy'.
Hard to understand why it should be a modern fake, because genuine bronzes of the Tetricus's are relatively cheap, but I have found odder circumstances than this, with ancient coins!

This is the other side

Obv. C PIV ESV TETRICVS CAES
Rv. SPES AVGG Spes advancing left holding flower lifting skirt
Sear 11292 RIC 270
AD273-74
According to Sear minted either Mainz or Trier

Looks almost as though it could be double-struck or over-struck onto something. Can often be difficult to tell between official and unofficial with these as the line is blurred. Don't think I'd disagree too strongly if I saw it described either way.

Barbarous contemporary copy?
I am, nevertheless, still tempted to think that it is of modern manufacture.

I am not convinced it is of ancient manufacture....I am feeling it is modern piece....

England didn't exist as a nation back then.

The Gallic empire by the time of Tetricus I and his son (http://en.wikipedia.org/wiki/Tetricus_II) had shrunk in territory but still possessed northern Gaul, including the the major frontier cities of Trier and Cologne.

And so Tetricus & son cannot be referred to as "Britannic" as Carausius and Allecus were 22 years later, though he too had possession of northern Gaul for a while.

The empire of Postumus to Tetricus I, as we know, is known as the "Gallic empire". http://en.wikipedia.org/wiki/Gallic_Empire

The coin in question is real but a typical contemporary imitation, and a nice one, done by local Romans, and this imitating seems to occur along the frontiers, from southern Britain to the Rhine.
It seems to have had its Patina zapped off by over cleaning unfortunately.
Onviously the imitators did not know Latin well enough to know what the abbreviated letters stood for.

It may be surprising to think that not every citizen or Slave in the empire knew Latin.
From the mid 3rd century the empire in Gaul and Britain was not a land of glistening marble cities were everyone was semi-divine Polymath and knew every single Latin work every written.

By that time a lot of cities were being walled off, both due to the civil wars and to "Barbarian" raids.
Civic structures, built a hundred years earlier, were decaying. And this impoverishment would be reflected in the knowledge locals and Slaves had of proper Latin.

To add to this, the former lands of the Iceni in southern Britain seem to have been deliberately neglected after the failed Boudiccan revolt of 61 A.D.
Venta Icenorum seems to also have been a walled settlement, but not much more. http://en.wikipedia.org/wiki/Venta_Icenorum

This was the frontier region, later known as the "Saxon Shore" from which such contemporary imitations of Gallic Empire coins, came from. So knowing that the local populace had been deliberately impoverished it would not be surprising if not all the locals knew Latin properly.

Contemporary imitations from the posthumous issues of Claudius II to Tetricus II are labelled "Barbarous" but the actual "Barbarians" of Germany and eastern Europe had no interest in making coins of their own, rather they preferred Loot such as Bullion and Slaves.