The phrase "a mainstream of" is correct and can be used in written English.
Generally, it is used to refer to a large body of people or things, often with similar beliefs, attitudes, or activities. For example, "The new film appealed to a mainstream of moviegoers."
One can only assume that large numbers of people – in Eastleigh anyway – are simply voting against a mainstream of which the Lib Dems have become a part.
When Scott wrote Waverley - which began, I believe, a mainstream of British fiction that is still very strong - he subtitled it 'To 60 years since'.
Where once the Strokes were a welcome deviation from a mainstream of slick pop, rap metal and electronica, now they are part of a wave of indie-minded, guitar-heavy bands, which they helped usher in.
Although management of the huge data sets generated poses challenges, this technology is becoming a mainstream of transcriptome analysis.
In a mainstream of a large-scale synthesis, soft chemical methods can be chosen due to a low growth temperature and a good scale-up potential [2, 3].
Concentrating solar power (CSP) is a mainstream of solar energy utilization, and thermionic emission is a potential way to convert concentrated solar radiation into power with a theoretical efficiency of 50 70%, surpassing both Shockley-Queisser limit and photo-thermal limit.
To the traditional Christian bookstores and retailers a mainstreaming of the market is not entirely welcome.
Unfortunately the language used in SFDRR does not reflect a mainstreaming of existing lessons, despite calls found in the literature and the HFA mid-term review.
I think we're gonna see a mainstreaming of that, brands are going to try to get a piece of that.
Bernstein's alliance with Wallach marks a mainstreaming of her ideas inside the Beltway.
For those who follow the private equity world closely, it's all part of a much larger trend: a mainstreaming of the industry.
