I think that you will find that BT, if they get to find out, will deny you the opportunity to do this. The reason is that those concrete manhole covers are designed for paved areas and not areas subject to passage by vehicles. I think (but I am not sure) that they are typically rated at 2 tonnes.
The problem that BT will have is that they can't control what then goes over the manhole cover - a 15 tonne lorry?
The way I would try and do it (assuming that driving in / out doesn't have to involve passing over the cover itself) is to make the application to the local council but remain stuum. If they say it is necessary to contact the long list as above of utilities, you might just as well stop there.
If they don't, you may well find no-one realises.
In the later event that a cover got broken I suspect (but again not sure) that it couldn't really be down to you. Afterall, you were given permission.