You can arm police to the teeth but the reality is it would make very little difference to an attack. Terrorists like the Mumbai group are suicide attackers. There is no escape plan, the attack is to kill as many as possible regardless of age or sex and then die themselves. Western civilisation is completely open to such.
lmagine 10 Derrick Birds armed with AK47's and explosives and splitting up into 2 groups or even pairs and then hitting various London targets on a busy Saturday afternoon. You simply cannot defend against such an attack. All you can do is damage limitation but that in itself is also limited by the very nature of the attack.
This arming and training of police by the SAS press release is just the Government saying 'We are doing something' because they know, as do the police, that there is little else they can do.
One wonders how you can train for such an incident as Mumbai in somewhere like London? The police may have access to more powerful weapons but actually using them would only be adding to the public casualties. Their recent exploits involving marksmanship hasn't exactly been inspiring h/t Ambush Predator
Seeing as they already have a vast array of firearms, one wonders what these more powerful weapons would be .... .50 cal? 20 mm cannon? 30 mm cannon? The armed forces are taking cuts because it seems we have another army ... called the Police Force!
Who should we be more afraid of ... the foreign 'terrorists' (who don't seem remotely interested in the UK) ... or the Police