Nigel Farage has said he felt "awkward" on a recent train journey in central London when he heard only foreign languages spoken by his fellow passengers.
Pressed on the immigration themes in his earlier speech at a press conference during Ukip's spring conference in Torquay, Mr Farage denied he felt people should be forced to speak English on trains.
But the Ukip leader said: "I got the train the other night, it was rush hour, from Charing Cross, it was the stopper going out. We stopped at London Bridge, New Cross, Hither Green.
"It wasn't until after we got past Grove Park that I could actually hear English being audibly spoken in the carriage. Does that make me feel slightly awkward? Yes.
"I wonder what's really going on. And I'm sure that's a view that will be reflected by three quarters of the population, perhaps even more.
"That does not mean one is anti immigration, we're not anti immigration, we want immigration, but we do absolutely believe we should be able to judge it both on quantity and quality."
In his earlier keynote speech, Mr Farage said: "The fact that in scores of our cities and market towns, this country in a short space of time has frankly become unrecognisable.
"Whether it is the impact on local schools and hospitals, whether it is the fact in many parts of England you don't hear English spoken any more.
"This is not the kind of community we want to leave to our children and grandchildren."
Answering further questions at the press conference about why he felt awkward Mr Farage said: "Because I don't understand them."
And he added: "Not more English - English.
"I'm not saying people on trains should be forced to speak English... but what I am saying is we now have nearly 10% of our schools in our country where English is not the primary language in the homes those children come from.
"I think that is a concern and particularly as if you compare us to comparable countries in northern Europe. We have had a record of integration and race relations and religious tolerance that is not met, or even come close to, anyone else in Europe.
"So I do think the integration message is actually very, very important. If you have open door immigration we have seen on the scale since New Labour came to power in 1997, it makes that transition very much harder.
"The answer is I don't feel very comfortable in that situation, I don't think the majority of British people do.
"It doesn't mean I am against anybody from different backgrounds or different cultures, far from it. I want us to have a sensible open minded immigration policy.
"What we have got and what we have had, and what we continue to have when it comes to the EU is wholly irresponsible and I think it has done great damage to the cohesion of our society."
In his earlier speech, Mr Farage said his party represented the biggest threat to the political mainstream for a generation.
The Ukip leader said his party would continue promoting immigration as a key issue ahead of the European Parliament elections on May 22, insisting the main parties had failed Britain.
And he told the conference: "Our ruling classes have lost confidence in this country and that is why they have sold us out and it's cost us money, it's cost us influence and it's cost us self-respect."
Broadening his themes on the failure of the existing political establishment, Mr Farage said the current regime had proved itself "unfit" during the floods crisis which hit Britain.
He called for a public inquiry into what went wrong at the hands of the Environment Agency and criticised the handing of powers to quangos which are "generally run by former failed politicians".
Mr Farage said: "It is astonishing to me the Environment Agency's priorities for nearly 10 years have been to maintain the EU habitats directive, to put the interests of wading birds, molluscs, beetles and water voles above the interests of farmers and householders on the Somerset Levels.
"They have even effectively been stopped from dredging because that is now classed as industrial waste and costs a lot of money."