The European Commission is to step up its investigation into allegations that UK customs officials are illegally harassing cross-channel travellers looking to take advantage of cheaper alcohol and tobacco prices.

Hundreds of travellers from the UK have complained to the Commission, saying that customs officers, in their efforts to clamp down on smugglers, are victimising legitimate cross-border shoppers.

The UK government has been given two months to respond to the EC's questions. The investigation could ultimately lead to the EC bringing a lawsuit against the UK government before Europe's highest court.

Travellers from the UK are allowed to bring back low-priced goods bought in other EU countries provided they are for private consumption. It is only the resale of the goods which is illegal. "The fight against fraud must not be used to dissuade people from shopping," said EU Internal Market Commissioner Frits Bolkestein. "Cross-border shopping is a fundamental right under EU law and should not be regarded as a form of tax evasion."

In its defence, the UK government says it is merely looking to cut down smuggling. Last year, it allocated an additional £209m to stricter policing in the London area alone.

However, in July, the UK High Court ruled that methods employed by customs officers to crack down on smuggling are in breach of European Human Rights Convention. The court said that officers have no right to conduct stop-and-search checks without "reasonable grounds".

The EC intends to question some of the practices used by customs officials but a spokesman for the UK mission in Brussels insisted that UK customs was implementing the EU rules correctly.