I get my BB through a BT phone line via a D-link. Would I be better off just going with BT? Its cheaper (but dont know for how long)

I never have any problems but wonder what would be the advantages if any, other than cheaper?
Could I get faster BB Or is it standard when its D-link? As you can see I'm a bit rubbish at this stuff.

Isn't d-link just the maker of the router ?, who is your internet service provide ISP, the company you pay for broadband ?
You can't have Virgin national broadband over a BT line anymore, they have stopped offering it, so if you want Virgin broadband you need to be in a cable area,
If you have line rental from BT and broadband from another company ( that supplied the d link router ) you may get a better deal with a line and broadband bundle from one company , BT or someone else, best to check you are not in a minimum term contract as the early termination charge may be more that any saving made by changing company

Its a gizmo you have plugged into the phone line that connects to your router and then to the PC/laptop ?

I am with Virgin and have been for years.
Sadly I am not in a cabled area.

So you think changing would be the better option?

I think the D-link you are referring to is in fact a microfilter.

Change if you want. There are many other companies besides BT offering ADSL. The service you get is likely to be similar from all of them, with the only noticeable difference being price and customer service.