Microsoft DirectAccess not working with HG633 router

I'm having problems accessing my work network using MicroSoft DirectAccess. This works fine if I connect to a giffgaff 4G router instead of via my TalkTalk router, but won't connect using my TalkTalk broadband.

Are there any router config changes that would make this work, or a firmware update that may help ? I currently have the HG633 router running software version v1.22t

I see that firmware updates have helped other people with VPN issues in the past.