If you do a Manual Search, the FVP 4000T opens the Search screen with TRANSMISSION pre-set to DVB-T. This means that it is searching for SD stations and it will not see HD stations.

If you want to do a Manual Search for HD stations you need to set TRANSMISSION to DVB-T2.

When doing a Manual Search be sure to delete the specific TV stations that you wish to replace. IF you don’t you get a message saying that the stations have been found but, when you save, the old station is not overwritten.

If you do an Automatic Search, it seems that the FVP 4000T does two scans – presumably one for SD stations and one for HD stations.

See Can FVP 400T receive the new Freeview signal?

Thanks to Luke and SSThing for pointing this out.