Try to remember these key points:

1. Don't panic until you've seen a solicitor
2. Don't say anything until you've seen a solicitor
3. Don't sign anything until you've seen a solicitor
4. Don't write anything until you've seen a solicitor

Simple.

Just like the movies, you do have the right to remain silent.
Don't say anything to the police, and don't get pressured into answering questions. There's no such thing as a friendly chat with an arresting police officer so be safe and say nothing at all.

You should request a solicitor to visit you in the police station as soon as humanly possible and ask for them to be present when you are interviewed. Don't let them fob you off. It's one of your rights and it's free.

The police can only keep you banged up for a limited period of time - normally a maximum of 24 hours or 12 hours longer for a serious arrestable offence. So try to remain calm. Make sure you know why you've been arrested, and that the correct time of your arrest is on the custody record.

The police can perform an 'intimate body search' on you if an officer (at least the rank of Superintendent) has reason to believe that you have concealed Class A drugs - such as heroin and cocaine, but not cannabis on you and that you are in possession of the drugs either with intent to deal or with a view to committing a customs offence. So be sure to mention that before they get the rubber gloves out!