I'm on an outdated OVP O2 tarriff (£45pm -400xnet) which is long
overdue for an upgrade (p990 which I can get for free),

I am keen to stay on an O2 tarriff with Orange.(0845/0870 inclusive).

The problem is that while Orange will let me stay on this Tarriff at a
reduced cost - £25 (quite reasonable), I need more minutes and would
have been happy to pay a similar price as the current O2 tarriffs cost
e.g. £40 for 800 or 1000 mins (18 month contract).. Orange says they
cannot do this.

Do the price match tarriffs that Orange now offer, reflect the original
phone companies pricing policies. E.g. say a price match for a 3
tarriff - will it have the out of price calling costs/texts/etc for 3
or for Orange? Is there a way I can get Orange to agree to my request?

There are other less desirable solutions - involving getting a second
contract..