Thanks for all the help.  Too many to mention all by name but the
following method gave me the results I needed.

First of all I converted my polygon to points using the Any Shape to
Point script (found on the ESRI website).  I then  found a free trial of
a program called Tralaine on the web that allows the conversion of data
in different projections.  I have now added the output theme in decimal
degrees to my project.  All that remains to do is find a script that
adequately converts my point theme to a polygon.  I have tried several.
Connect the Dots from the ESRI website was the most successful, although
I don't have enough room on the computer to do this.  I may try to find
a way around this.  The problem is that the polygon shape - an outline
of the UK is highly convoluted and I assume difficult for a script to
easily convert.

However, as the Any Shape to Point script results in a table with the
distance and bearing between adjacent points I wonder if by using this
table with the decimal degrees pasted in over the OS grid refs, it would
be able to deal with it better that way.

Any ideas?

Thanks again for the help,

Catriona Dryden
-------------------------------------
Catriona Dryden
Marine Projects Officer
Centre for Marine and Coastal Studies
(A division of ERC)
Port Erin Marine Laboratory
Port Erin
Isle of Man
IM9 6JA

Tel: +44 (0)1624 831018
Fax: +44 (0)1624 831043
Email:   cdryden@LIV.AC.UK
Website http://www.erconsult.co.uk