First up i would not of gone with TalkTalk on a mission critical connection that you need for work as TalkTalk are a domestic broadband supplier .
But that said , you should try members forum and see if thay can support your requirements .
We had been with Orange for years as domestic customers and did not have a problem. Same if we travelled to relatives places who don't use the net for work purposes and again didn't have any problems.
We asked Talk Talk before we signed up about connecting to work and wasn't told anything which suggested it would be a problem.
I went over the contract and nothing has been mentioned about VPN or blocking VPN connections.
It was only when we connected a few days ago to Talk Talk that connecting to the work VPN became a major issue.
We have asked Talk Talk and posted on their forum and nobody can explain what the problem seems to be whether it's a Talk Talk issue or a router issue. If it's the router then I could go out and buy a netgear one which should solve the problem. But I really need to understand the root of the problem first before I spend money resolving it.