Hmmm, an interesting collection
Bottom left I am certain is a Roman silver denarius, and middle left appears Celtic in origin. In fact, top left looks Roman as well. Good haul fella!
( jim_bob can herd cats., Thu 13 Nov 2008, 11:55, 1 reply)

as you are interested :-)
they are in order:

Denarius of Antonius Pius
English jeton (counting token)
Elizabeth I three pence
Edward I penny
George II sixpence
Another Edward I penny
Ancient British unit of uncertain tribe (very rare)
Commonwealth penny
Roman coin of Constantius II
Henry II penny
Elizabeth I two pence
George II shilling
Roman coin of Constantinus I (Constantine)
Edward I half groat
Elizabeth I three half pennies

2 and a half years of coming home soaked, freezing and covered in mud...
( stopmeandslapme Cometh the hour, cometh your mum, Thu 13 Nov 2008, 12:07, closed)

Are they worth much?

(oneinthepink is at your cervix m'lady, Thu 13 Nov 2008, 12:08, closed)

Not really
I reckon the Ancient British one may be worth £200 or so, the others, no more than £30 each.
( stopmeandslapme Cometh the hour, cometh your mum, Thu 13 Nov 2008, 12:10, closed)

You may be able to identify that coin
Based on the tribes that inhabited the area before the Roman invasion in AD43. Given that the idea of coinage was copied from the Romans, it'll only be comparatively recent in terms of the period of the iron age it comes from.
( jim_bob can herd cats., Thu 13 Nov 2008, 12:21, closed)

There are some examples
on the celtic coin index:
www.finds.org.uk/CCI/details.php?coin_num=03.0526
www.finds.org.uk/CCI/details.php?coin_num=03.0107
www.finds.org.uk/CCI/details.php?coin_num=02.0208

When I found it the tribe was "uncertain" but now apparently the tribe is Trinovantes.
( stopmeandslapme Cometh the hour, cometh your mum, Thu 13 Nov 2008, 14:41, closed)