I don't think there is any organisation you can get to confirm this.
Frankly if you have been with the same company since 2000, this (9 years with current employer) should be good enough for any prospective employer to decide whether to interview you or not, and it is clearly some petty HR rule that says 'ask for the last 12 years job history' that is driving this.
You can probably get confirmation from your current employer about where you previous job was - they will have asked for references and it should be in your personnal file. No, I'm not being daft - invent a plausible reason for needing to know like - 'I've got a query about my NI record with the Pensions Service and they want to know who my last employer was' That should do it without raising suspicions.