I did check on Nationwide after my post and realised that they didn't offer business banking. May be that is what makes them a "building society" then apart from obviously their mutual status? As a personal customer they seem to offer just the same facilities as NatWest but a lot more cheaply and efficiently.
NatWest have dreadful rates of interest on their online savings account and appalling fees for withdrawing cash on the credit or debit card or making purchases with the said cards overseas. Withdrawing cash on a Nationwide Visa blue debit card is fee free overseas but costs 4.65% with Natwest subject to a £2 minimum. Even using a credit card in a store with NatWest costs you 2.65% foreign exchange rate levy.
As to calling 0870 with Alliance & Leicester you can call a bit cheaper with
http://www.dialaround.co.uk/rates.php and their 5p per minute 0844 number for dialling "national rate" 0870 numbers - 0844 566 7676. You waste may be 15 extra seconds of call time having to call via this number but still a good saving of 2.5p per minute on say a 15 minute call.
Or set up an account with
www.18185.co.uk which costs 4p connection plus 4p for the first minute to 0870 numbers and then 4p per minute thereafter. This makes them cheaper than dialaround if the 0870 call lasts 5 minutes or more.
I can't believe there isn't a geographic number for A&L Business banking somewhere?