JAR-FCL says with regards to P.1 time for ATPL issue:
((i) 500 hours as pilot-in-command under supervision;
or
(ii) 250 hours either as pilot-in-command;
or
(iii) 250 hours made up by at least 70 hours as pilot-in-command and the necessary additional flight time as pilot-in-command under supervision;
If you have 250 hours proper p.1 (maybe been instructing or so?) you won't need any P.1/s hours countersigned, as they are not required for license issue. They just count towards your total flight time just as dual and P.2 time.
If you are relying on your P.1/s time to get an ATPL issued you will either need your logbook signed or get a letter from your company (it seems the UK CAA at least are willing to accept this).
Hope this helps.