If there are no entries on the PNC there will be no entries on the Warnings Index in respect of any criminality or concerns from a UK perspective.
The Warnings Index is used primarily by UK Border force for immigration purposes and will contain information about people of interest received via alerts from other countries e.g. terrorism watch lists, interpol notices, ...
Unless you have committed a very serious crime overseas and it has been flagged to the UK authorities, you will be OK.
(Note that the UK authorities cannot check criminal records in other countries if you are not an UK national)