Citizen's Arrest

What are the rights of members if they catch a thief red-handed on their premises – can they carry out a citizen’s arrest or restrain the thief physically, or should they just take a description and call their local police?  And what are their rights when someone enters their shop and tries to sell a book which they know or suspect to be stolen? 
As with all these things, the answer is to be very sure of your ground and very careful, but we hope that the following will be of some help. 
Stealing from a shop is classified as theft.  A person is guilty of theft if he or she dishonestly appropriates property belonging to another with the intention of permanently depriving the other of it; and "thief" and "steal" shall be construed accordingly.
Theft is an arrestable offence.  An arrest in some circumstances may be made by any person.   Anyone may arrest without a warrant anyone who is in the act of committing an arrestable offence, or anyone whom he or she has reasonable grounds for suspecting to be committing such an offence.  Where an arrestable offence has been committed, anyone may arrest without a warrant anyone who is guilty of the offence, or anyone he or she has reasonable grounds for suspecting to be guilty of it. 
A citizen’s powers are not as great as a constable’s and a citizen may become liable to civil action if he or she acts incorrectly.  The following case illustrates the difficulty: 
A person, whilst in a shop, was observed to pick up a chocolate bar and leave.  A store detective, shop assistant and onlooker followed and a struggle took place, during which the assistant and onlooker were assaulted.  The person was arrested and was subsequently charged with the theft of the chocolate and two charges of "assault with intent to resist arrest".  At Crown Court he was found not guilty of the theft, but guilty of the two assaults.  He appealed against the convictions on the grounds that for a member of the public to make a lawful arrest, an arrestable offence must, as a pre-condition, have been committed.  In this instance, no theft had been committed (he had been found not guilty of theft) and therefore the store detective, assistant and onlooker had no valid power to arrest.  If this was correct, then the person could not be found guilty of using force to try to prevent an unlawful attack on his person.
Attempting to sell a stolen book may be an offence of handling stolen goods.  This is a complicated offence and, for a citizen to make an arrest, he or she must be sure that the property is stolen and that the seller knows it is stolen. 
In the interests of your safety and to improve the chances of convicting thieves, the advice that we have received is that you should always call the police if at all possible.  If a citizen’s arrest is made, then safety should be considered first along with the rights of the suspect.  You should if practicable tell the accused person at the time of arrest that he or she is under arrest and give the reasons for your action.  If an arrest is made then only such force as is absolutely necessary may be used.  You should treat the accused person with consideration at all times.  You should keep the accused person under constant supervision until the police arrive; this is to avoid escape, to stop disposal of evidence and to prevent physical harm.  If two or more persons are involved, you should try to keep them separate. 
However good your physical security measures are, the best form of security is for potential thieves to know that they are being watched – greeting them as they enter the shop and asking them occasionally if they need help are excellent deterrents (as well as good ways of annoying innocent customers).  And, finally, remember that your split-second decision may be reviewed by a court weeks or months later.