It was a lie, EU citizens in the UK earn significantly more than the locals. If I wanted to be a member of the underclass, say a cleaner, I’d be in Germany, where I wouldn't have to pay 6K£ for pregnancy and 12K£pa to send a child to a half-decent primary school.
EU citizens living in the UK on average earn a lot more than the locals and are better qualified. So saying that migration from the EU was driving down wages was indeed a lie.
But even if we assume that the UK had been swarmed by millions of illiterate cretins, there isn’t any evidence anywhere in the world that immigration suppresses wages permanently (there may be some temporary short term effects, but before, you say anything, the UK has been in the EU for decades, so we are indeed in the long run).