Spoken English is following the lead taken by Star Trek to boldly go in search of new grammatical rules.

A vast collection of British conversations containing 11.5 million words has uncovered an invasion of split infinitives since the 1990s, along with a growing tendency to put "like" at the start of sentences.

Use of the split infinitive, as exemplified by the famous Star Trek introduction "to boldly go where no-one has gone before", has almost tripled over the last three decades, the research shows.

Linguists who analysed conversations recorded on people's smartphones discovered that the split infinitive rate rose from a mere 44 words per million in the early 1990s to 117 per million in the 2010s.

Split infinitives squeeze an intervening word between the word "to" and the verb - something many traditionalists would consider a serious grammatical error.

Examples cited by the researchers included "to just go", "to actually get" and "to really want".

Dr Claire Dembry, principal research manager at Cambridge University Press, who helped set up the Spoken British National Corpus 2014 project with experts from the University of Lancaster, said: "Learners of English deserve to be taught in a way which is informed by the most up-to-date research into how the language is used in the real world.

"The rise of the split infinitive is just one example of language phenomena which some commentators might not like, but which are becoming a normal part of everyday speech.

"Language teaching should reflect these changes, which can only be observed in a corpus such as this."

Another change imported from America and highlighted by the research is the habit of starting a sentence with the word "like".

The study found that the frequency of this usage of the word soared from 160 per million sentences in the 1990s to 625 per million in the 2010s.

A further Americanism was the substitution of "awesome" for "marvellous", a word that had fallen out of fashion.

The conversations were gathered between 2012 and 2016 by members of the public during everyday encounters with family, friends and colleagues.

Participants included a newly wed couple reminiscing about their recent honeymoon, students drinking in their halls, a father and daughter chatting in a car, and grandparents on a family visit.

The researchers compared word use and grammar in the conversations with an earlier collection of recordings from the 1990s.

Project leader Professor Tony McEnery, from the University of Lancaster, said: "The launch of the Spoken British National Corpus 2014 is an important moment for the study of spoken English.

"Never before has it been possible to compare millions of words of spoken English across decades in this way.

"This will help linguists to understand better the changing nature of English speech and help a new generation of learners of English in the modern world."

Anonymised transcripts from the conversations are to be made publicly available online free of charge.

Research papers based on the collection will be published in the International Journal of Corpus Linguistics later this year.

A total of 672 "speakers" recorded around 1,000 hours of conversations for the project.

The research hinted at one trend that has been a particular bug-bear of BBC Radio 4's John Humphreys.

The Today programme presenter has railed against the use of the word "so" at the beginning of sentences, especially by academics.

Mr Humphreys, whose best-selling book Lost For Words talks about the decline of the English language, has described it as a "noxious weed" invading every day speech.

The linguists found that since the 1990s, general use of the word "so" had doubled from 1,222 per million words in the 1990s to 2,367 per million.

Robbie Love, a PhD student from the University of Lancaster who took part in the project, said there did seem to be evidence of the word increasingly being planted in front of sentences.

Explaining the phenomenon, he said: "Generally speaking over time the more that words are used the more they become weakened and more ingrained. They lose value, and become weaker and more common."

He added: "I don't lament these changes. Language has always changed; it's perfectly normal.

"A lot of people get overly worried about this sort of thing. If words associated with the US are becoming more common I wouldn't say that's ruining the English language or making us more American.

"People shouldn't feel threatened by these changes. They've been going on since time began."