Re: Experienced this myself...
I'd have to check on Ireland specifics but in the UK only the police can force you to do this. You're employer can ask you, and you can refuse. However this may put you in breach of your employment contract and be used as grounds for dismissal.
If you have 'given consent' when signing your employment contract you are still able to withdraw that consent at anytime. If someone were to man-handle you at this point they run the risk of committing assault etc. if someone has withdrawn consent to search and there are reasonable grounds for suspicion then calling the police is the next obvious step.