British Christmas Tree Growers Association secretary Harry Brightwell has said street-side sellers are damaging the reputation of his grower members.
"On the roadside you don’t know where they are sourced from or even if they were bought and not stolen." He said complaints should go to local councils.
Brightwell said Google and Amazon had been exposed for avoiding paying UK tax, but black market sellers still flew under that radar.
"These sellers may not be paying taxes. Nurseries pay taxes and white man van doesn’t. The public can act by buying from the people who pay tax – it’s easier than avoiding Google or Amazon."
He added that there’s "still not enough home-grown from UK market and exported needed. If it becomes an over-supply will hit price."
He said current season needle necrosis was more of a problem in 2012’s wet season, with five per cent of trees hit but has been "not much reported this year". Affected trees would not reach the consumer, he added.
He added that "supply, demand and prices are similar to 2012, which is good news for the public, although growers overheads have gone up". Sales of real trees are 6m to 8m a year.
Five London garden centres led by North One are campaigning against rogue Christmas tree trading.