Ralph, not far off actually.
what we have found is that the switch is by default using CDP, and the vlan associated with the CDP is VLAN100 (default Cisco). even though we deleted VLAN100 from the switch the CDP Field still showed it. The phone was booting and must have been getting the CDP because as it was going through the boot process we could see the vlan was going to VLAN 0? anyway when we turned CDP off on the switch all was ok. We also left CDP on but deleted the VLAN number which had the effect of putting a 0 in the VLAN field on the switch, which we couldn't do manually as VLAN 0 is not a valid VLAN?? Anyway, with CDP on and VLAN field set to 0 the phone then booted with VLAN NONE, and away to go.
Interestingly enough none of this affected the 5312 handset that we had connected too.
Thanks for the help all.