Immigration officers have been accused of clamping down on non-European Union nationals which has led to business executives being detained at airports and at least one refused entry.
Incidents include a Swiss banker put on a plane back to Switzerland, US executives interviewed by officers at Heathrow and the chairman of a European bank held for two hours at Gatwick on Friday.
Leading City lawyers are worried about the impact the "heavy-handed" policy may have on the international business community. The checks are thought to be a response to the abolition of border controls within the rest of the EU.
Immigration lawyers , representing the cream of the City's international corporate businesses, say their immigration "troubleshooting" for leading clients has increased since the change in EU border controls.
Elsbeth Guild, a lawyer with Bailey's Shaw and Gillet, said: "I was asked to advise a company based on the continent which had sent one of its employees, who is not an EC national, to the UK to give a lecture. The person was refused permission to enter the UK as a visitor because the immigration officer decided that the lecture was work. He was sent back on the same plane."
Other leading firms, who asked not to be named, said a number of their corporate clients were "angry" at what appears to be happening at Heathrow, Gatwick and Stanstead airports. Several said City's international reputation could suffer.
One US executive arriving to work on a computer contract was recently refused entry at Heathrow. He had never been refused entry in more than a decade of travelling to Britain.
Julia Onslow-Cole of Cameron Markby Hewitt, said that on Friday the chairman of a European bank, a non-EC national, was detained at Heathrow by immigration for over two hours. He was not questioned but kept alone in a room. She said the chairman described the incident as "incredibly embarrassing". He had never experienced any problems in numerous other visits to Britain.
She said that some of her firm's leading clients had been "stopped" and that the action used by immigration officers had been "heavy-handed". But the Home Office said there was "no change in the practice or procedures" being followed by immigration officers.
According to current UK immigration rules, a visitor to the UK must not intend to provide services in the UK. However most lawyers acknowledge that any business visitor is going to be providing something which could be classified as a service. It is this strict adherence to the rules that is worrying the City.