Just as an update, I have been at a client this week using the same laptop I use at work and the client's wireless connection. Apart from it being quicker than the office internet I have had no problems posting on here, still using IE8
I presume it must be a local firewall issue, although I don't think it would go down too well if I was to ask them to sort out the firewall at work so that I can post on here when I should be working!
I've also had problems posting to another forum that I also use, but again only on IE8 and where ever I post from (home or office). When I switched to Chrome at home I experienced no further problems.
Is Chrome too lax in its security or is it IE8 that is too strict then?