Yes you can - but there are rules, depending on whether you want to fly in EU Member States or non-EU Member States.

Rules For UK Drone Operators Flying In EU Or EASA Associated Member States

Registration: UK operators must register with the Member State they wish to fly in.

Open Category: If you require an A2 CofC to fly, then you need to obtain a new A2 CofC in the EU Member State you wish to fly. Once you have this, the European version of the A2 CofC will be valid in all other EU Member States and EASA associate Member States.

Specific Category: Some nations will let you fly with your valid UK Operational Authorisation - although you will need to amend your Operations Manual accordingly. Other nations, require you to complete a separate GVC and apply for a new Operational Authorisation. Check with the relevant aviation authority before your operations.

Rules For UK Drone Operators Flying In Non EU Or EASA Associated Member States

You must comply with the requirements set out for UAS operations within that state. Operators should consult the guidance documentation that has been prepared by the relevant National Aviation Authority.