LJ - I thought speed was life in AAC? The Me109 only had about 5 mins of effective dogfighting in 1940 because it was fighting a long way from home. Drop tanks came in to allow long range transit. It depends where fuel is used first - ideally from drop tanks but within the aircraft is a different matter for balances and reliefs.
If a Typhoon was scrambled from the UK to intercept an unknown contact fuel is not an issue! There are plenty of places to divert into on a fuel priority in the UK - St Mawgan all the way up to Kinloss/Lossie, or at a stretch Stornoway or Wick. There is a tanker on standby at Brize and more 'Q' jets that will take over if the 1st wave has to come back in. The UK isn't guarded by just 2 guys in immersion suits sitting in a Lincolnshire shed!
We're getting 9 MRA4s at the moment - we've got fewer C-17 and Sentinel - and they're out in theatre. No reason it shouldn't see action...