Something has to give - the money just isn't there to replace the UK armoured forces AND do everything else.
JTO makes some good points but it's hard to envisage a fight were a 100 or so new heavy tanks would make a difference. If you're up against the Russians you'd need a LOT more, and anyone else is along way away - just transporting a large tank force would be a nightmare. I can't see the Brits fighting the Chinese on land either - so who is left? TBH I've always felt the British Armies real lack of ground based AA to cover armour and infantry has meant they could be in for a nasty shock against some opponents