The home secretary, Theresa May, said officials from the UK Border Agency were taking steps to remove Salah from the country. She said an investigation had been launched into how he managed to get into the UK.
"We do not normally comment on individual cases but in this case I think it is important to do so.
"I can confirm he was excluded and that he managed to enter the UK. He has now been detained and the UK Border Agency is now making arrangements to remove him.
"A full investigation is now taking place into how he was able to enter."
His solicitor, Farooq Bajwa, said Salah had "no knowledge" of a travel ban and had made "no attempt" to conceal his identity when he entered Britain.
Salah's lawyers have denied the charges, noting that his political work in Israel is carried out in full knowledge of authorities and that his movement has never been banned.