Skilled migrant workers have protested against rule changes which they fear will force them out of the UK.
Protesters urged the government to "keep its promise"
Accountants and businessmen were among those chanting "Home Office, keep your promise" outside Parliament.
The criteria for the Highly Skilled Migrant Programme were changed last April, as part of moves towards a new points-based immigration system.
But some workers who have lived in the UK for years fear they will not qualify and say they feel betrayed.
Hanish Sevak, 34, from Gujarat, India, arrived in the UK in March 2005 and works as a business consultant for British Gas in Leicester.
At the time his ten years' professional experience stood him in good stead and he believed he would be offered indefinite leave to remain after four years.
Now he says he has to reapply under new rules which favour younger workers - so, he says, his age and experience count against him.
He told the BBC News website he sold off his belongings, gave up an established career and uprooted his family to come to the UK, based on a commitment from "a responsible government".
Hanish Sevak said he gave up everything to come to the UK
"I liquidated all my financial assets ... all my life savings in order to reinvest in a life over here.
"They [the government] are basically creating a breach of trust. I was in a state of shock for some time. My daughters are too young to understand the implications but my wife is quite disturbed."
Deepak Gautam, 44, from Nepal and his wife Binita now live in Charlton, south-east London. He works as an accountant and also arrived in March 2005.
He trusted the word of the British government, but says he now feels "completely betrayed".
"When I heard these things, it was unbelievable."
Nigerian Camillus Osubor, 45, arrived in the UK in 2006 and has been working as an accountant in west London.
"I gave up all I had, I gave up my two bungalows, I sold my wife's business, I sold off all I had in Nigeria because I knew I could make a future in the UK," he said.
He said he was not against the UK changing its immigration rules, but it was "very unfair" to make them retrospective.
The Home Office said the new rules would benefit the UK economy and were based on requirements "which will best reflect success in the labour market".
But a spokeswoman said: "It is expected that the majority of HSMP (Highly Skilled Migrant Programme applicants) seeking to extend their stay in the UK will be successful.
"We have developed transitional arrangements to avoid disadvantaging those that fail to meet the new requirements, but are making a useful contribution to the UK."
She told the BBC News website that people already working in a skilled job, who did not qualify under the new requirements, may be able to switch to a different immigration category, such as work permits.