A temporary broadband service might not be practical. Some do monthly contracts, but then charge a heafty leaving fee if you leave within, say a year for example. It might even take more than 2 weeks to get up and running in the first place.
You could of course use an 0845 local rate access number but your phone bill could go through the roof even over just 2 weeks.
A temporary 0808 or 0800 dial up service should be easier, if you want a service that only lasts a month then some will do that for you.
Vispa will give you 80 hours of dial up for £7.99 per month, im pretty sure there's no annual contract with that, but you should check.
I'm sure there are many others.