AFTER just 20 stormy months of marriage, Britney Spears has finally had enough of her loser husband Kevin Federline.

For weeks they've been leading separate lives. Now their relationship is so strained that Britney - who is pregnant with their second child - has banished 28-year-old Federline to a self-contained "bachelor" flat in the basement of their Californian mansion.

Britney saw red after returning from New York this week to find her layabout hubby lounging around, drinking and smoking dope.

The 24-year-old pop star is said to hate seeing Kev's slacker mates near their eight-monthold son, Sean Preston, and has now decided she doesn't want him around her either.

Ominously, her spokesman refused to deny claims yesterday that she thinks her second marriage is over and wants a divorce. Even though the princess of pop is worth more than #65million, getting rid of Kevin may cost her as little as #190,000 and a half share of their Malibu home because of a canny prenuptial agreement.

According to a close friend of Britney, she had hoped that her marriage could survive at least until the birth of their second child in October.

We hear: "She wanted to wait, but their relationship has become so hostile she just doesn't see how she can make it work."

Things have been rocky for some time. She is said to have "cried for hours" after he spent Mother's Day with Shar Jackson, the mother of his first two children, rather than be with her and Sean.

Last week, before she flew to New York, Kevin went missing overnight. Britney got so angry that she bolted the front door and refused to let him in when he finally returned.

And at the weekend, she posted a poem, Remembrance Of Who I Am, on her website. With lines including: "No more chains that you gave me. My crown is back and it's way too high for you to be in my presence, especially my son", it seemed a thinly-veiled confirmation that she had finally lost patience with Kevin.

Our source adds: "Their relationship has totally broken down. Britney desperately wanted it to work and still does for the sake of their family, but she has had enough of him and the awful friends he hangs around with.

"But rather than move out, she has ordered him down to a separate flat in their basement. They have in effect divided their house."

It seems she feared that history was repeating itself. Britney's dad had a drink problem and her parents got divorced when she was young.

A friend says: "She can see certain things repeat themselves and that has made her even more determined to escape this marriage. She knows everything worked out well for her family because her parents made the wise choice to divorce."

Still, you've got to hand it to Britney - she made her second marriage last considerably longer than her first. That survived just 55 hours!