I'm not sure where in the Immigration Rules or in Primary Legislation it says that you can't have 2 concurrent visas. The quote by mulderpf is merely advice, which isn't law simply because UKBA says it - it must be included somewhere in legislation. If any one knows where it does, please put me right.
Of interest is this passage from Entry Clearance Guidance which seems to be similar to the OP's case:-
http://www.ukvisas.gov.uk/en/ecg/ecbasi ... #554475582
Other categories of entry clearance can be revoked by an ECO if the leave has not (not) been 'activated' by an Immigration Officer. Leave to remain and leave granted on an ICFN cannot be cancelled or curtailed by an ECO.
..........
Example 2:
The holder of work permit dependant leave arrived in the UK in 2008. His work permit dependant leave expires in late 2010 but he has now applied for leave to enter as a PBS Tier 1 Migrant. The ECO would not be able to cancel or revoke the work permit dependant leave. Cancellation of leave would fall to an Immigration Officer or in-country officials acting on behalf of the Secretary of State. The leave could not be revoked as it is not visit leave and has already been 'activated' by an Immigration Officer. It therefore acts as continuing leave.
So maybe when you arrived with the second Entry Clearance perhaps it was the IO's responsibility to cancel the first one and plonk an entry stamp on the second one. If they have not done that, I don't know where it leaves you in law vis-a-vis the first one - if it's not been cancelled it could be argued that it is still valid. However, for practical purposes, if you have an entry stamp that postdates the issue of the second visa, you can reasonably assume that the second visa has been "activated", wherever the IO put the stamp in your passport.
