Don't know if this helps Jem, but some companies that water cut Alu:
http://www.sheffieldwaterjetcutting.com/
http://www.waterjetcutting.co.uk/Abrasive.aspx
http://www.yorkshireprofiles.co.uk/m.../#.UQXNLWddVAo
http://www.ewlwaterjet.com/case_stud...ng_plate_c250/
http://www.safirewaterjet.co.uk/wate...ts-alloys.html
http://www.greatwesternmetals.com/
http://www.waterjet.co.uk/
Should save a bit of leg work