No visa for the countries of the European Union: valid identity card or passport.
With the Romanian identity card; also possible with a passport.
It is not possible.
An identity card is sufficient for a Romanian citizen.
No, because Montenegro is not a member of the European Union.
An identity card is sufficient.
No, you need a valid passport.
of course you can, Poland and United Kingdom are in European Union, so the passport is not necessary, polish ID or british ID is totally fine
For a Greek citizen: identity card or passport.
All Pakistanis do have a National Identity Card (NIC) and they are required to carry it around whenever they travel.
No you cannot enter without a valid Romanian Passport
Yes, You always need a passport (or EU national identity card) to get in our out of the UK.