As Whickerman states, it's perfectly legal to have designated smoking rooms in hotels, as long as these are clearly indicated:
http://www.smokefreeengland.co.uk/faq/exemptio ns.html
Smoking in the porch is not necessarily illegal. The law only relates to premises which are either 'enclosed' or 'substantially enclosed'. There are precise regulations detailing measurements but, as I assume that you don't carry a tape measure with you on holiday, these illustrations show structures where smoking isn't allowed (on the left) and where it is (on the right):
http://www.smokefreeengland.co.uk/images/galle ry/enclosedspaces.gif
Chris