It may depend upon your local transmitter. If your signal comes from the main regional transmitter you should receive all the Freeview channels, however if you are receiving from a local relay the channels will be much reduced. In any case you should always receive BBC1 and ITV1.

If you have recently been through DSO (Digital Switch Over) then you may still be in an interim stage where some of your Freeview channels are on reduced power because they could interfere with analogue channels in adjacent areas that haven't yet gone through DSO. But you should still receive BBC1 and ITV1.

DSO has been a long drawn out mess. We are years into the switchover but still have another year to go before it's finalised. Some countries did it for everyone on the same day (even big countries like Spain with all it's mountains!) so quite why the Government of the day decided on our 5 year switch over is anyones guess but it has provided a lot of people with well paid public sector jobs over a very long period.