The former La's frontman also labelled Powers a "spoilt brat" in his first interview in almost a decade.
Mavers was lead singer, guitarist and the songwriting inspiration behind the band, which scored a hit with There She Goes. But in 1992, with the La's on the verge of worldwide fame, he disbanded the group. He's since been hiding away and keeping his opinions to himself - until now.
Speaking exclusively to Access All Areas, Lee says: "John never learned anything from the La's. He's not talented. He never was. He had a bass guitar and a will when he first came along with the La's.
" To him it's all about money and looking good.
He's just like all the other pop stars - a spoilt
Cast's new single, Magic Hour, is released on Monday. The group have been accused of cashing in on the success of the La's.
But Lee says: "People aren't fooled. Anyone who saw the La's knows we were the real thing.
"I saw Cast on TV last week. It was comical. They never took anything from the La's. They never understood anything.
"Powers was standing against the wall, saying, 'Our records sell'. But look at what else sells, mate. They're just crap.
Daily Newspaper, one of the colour layers was offset.. badly printed..
"I haven't seen Powers since he left the La's. Enough said."
Lee accuses the rest of his group of being like "devil's advocates" once the La's got a record deal. "There was no solidarity in the band," he claims.
Father-of-four Mavers was released from his contract with record company Polygram on December 31 last year - and he's delighted about that.
"I was waiting for it for ages," he says. "It's great. There's £1 million debt, or whatever it's supposed to be, that's been terminated."
He adds: "The La's album is garbled.
"And they were able to do that because of collusion between other members of the band and the record company.
" I don't like any of The La's records.
"A band does not translate into the studio - it took me years to realise this." Still, fans have long been waiting for him to bring out another album.
It's never happened - and Lee says he's now concentrating on bringing up his four children.
And despite his dislike of the La's records, royalties from the band's discs especially There She Goes - are still flooding in.
"It's mostly £4,000 every three months, but last Friday I got £15,000 - and most of it is from There She Goes really" says song writer Lee.
"It never stops being on the radio. But I know that if it had been recorded correctly, it could have gone even bigger."
He still writes songs, but says nothing has been recorded because he "can't trust anyone" in the biz.
There have also been rumours of drug and alcohol addictions.
Mavers accepts he's had drug problems in the past and "tuned out" for a while. However, he says he's over it all now: "I couldn't run a family doing that."
Last night, Cast's management were unavailable for comment on Lee's accusations.