If you give us some more details, e.g. Make and model of set, Freeview or analogue, what channels you can get, what channels have "disappeared" and when it happened, then someone on here will no doubt be able to help you.
Are you saying somebody has pinched the 1 button from the remote? otherwise I can't see how the "option of BBC 1" has gone....
Assuming you have freeview then, as above says, just retune, until the full switchover has been completed later this year then you may find channels will change a few more times, if you get any strange problems with channels the first thing to do is retune the set.
Nope friends, this is what you do atalanta. Stage (i) ensure you have all channels selected (DTT?) as opposed to "favourites"; Stage (ii) Select Menu and chose installation, then chose "FACTORY INSTALLATION"; Stage (iii) Now from menu chose favourite channels - this avoids all that cr*p like cheap US jewellry sales etc. On our remote, favourites are chosen/deleted via a green button; Stage (iv) Name favourites channel e.g. FAVS 1 then keep pressing "back" to escape and save your work; Final Stage - Just press button called e.g. "list" to select FAVS 1. Select BBC 1 AND
AND THAT'S IT.