Due to the hidden nature of prostitution, reliable statistics on the numbers involved and their countries of origin are difficult to obtain. Estimates suggest that at any one time in 2003 there were approximately 4,000 victims of trafficking for prostitution in the UK. However, no research has been undertaken which would provide either evidence or provide a basis for estimates on the number of women working as sex workers in the UK whose countries of origin are (a) other EU member states (b) other overseas states.