Concerning tax, I think in this area you will proberly find that you can claim extra tax allowance, because you are going to have to provide things like heating and electric to charge/run your laptop, but a phone call/visit to your local tax office or even check there website should give you the information.
I am suprised that for a six month trail they going to all the hassel and expence of putting extra lines, prehaps you could suggest, that if they would like to subitise your phone rental and boardband rental, and of course pay for any phone calls made concerning business, would be an easier and cheaper alternitive.
Also check with your employers weather they are going to help towards the cost of electric/gas that you will be using, after all you will be providing an mini office at your home on there behalve?
also check your deeds or tenacey agreement, there might be a clause that might prohibit any business use from the property without permission, ( I had this on one property I owned, I wasn't even allowed to park a company/trade car/van on my drive!)
And if any damaged/loss of company laptop who's pays????
I hope this helps a little, but at least it bumps it to the top.