In addition to the obvious striking civil liberties angle (i.e. those who wish to smoke as a matter of personal choice have to do so outside whatever the weather), the amendment would have a positive effect on business, particularly pubs and clubs, and non-smokers.
Before the election, the Conservatives were campaigning to save the Great British Pub, but refused to acknowledge that one of the biggest factors in the decline of pubs is the Health Act 2006 (i.e. the smoking ban). Even my grandmother recognises this – and she's never smoked a day in her life!
By allowing separate smoking rooms to be installed (and these can be to a strict regulation to ensure that no under-18s or non-smokers come into contact with any second-hand smoke) pubs and businesses can increase trade and productivity respectively. Whilst impractical for some pubs, others would reap the benefits as they avoid the financial Armageddon and all-too-familiar wooden boards over windows. Businesses who don't need to send their employees into the cold/wet outdoors to light up will also see a rise in moral – and thus workload – as their employees can enjoy the habit in comfort.
Finally, by bringing smokers back inside in specially-designated enclosed areas, non-smokers will no longer need to pass the cloud of smoke on their way into, and out of, pubs, bars, shops, businesses and (my biggest gripe) courts. Before the ban, non-smokers had a choice – either enter the smoky atmosphere or not. Now, however, they are virtually forced to inhale the second-hand smoke, as they pass smokers on a near-daily basis.