By Martyn Herman

LONDON (Reuters) -A little over two weeks remain of the regular English Championship season but remarkably every one of the 24 clubs in the second tier could mathematically go up or down.

While the Premier League is widely-regarded as the best in the world, for pure excitement the Championship is unrivalled.

A marathon season comes to the boil this weekend with each club playing twice in the space of four days with key battles at the top and bottom of the table.

With four rounds of games left, leaders Leeds United and second-placed Burnley are level on 88 points and the favourites to gain automatic promotion, while Sheffield United in third spot on 83 have not given up hope of crashing the party.

With the teams finishing third to sixth entering the playoffs, the promotion door is ajar for a long list of clubs extending down to 14th-placed Sheffield Wednesday, who are 10 points behind sixth-placed Coventry City.

Unlike in the Premier League where the relegation places are virtually sealed with six games still to play, the battle at the bottom of the Championship is still raging.

Plymouth Argyle, who famously knocked Liverpool out of the FA Cup this season, are bottom but only three points behind Derby County who are 21st and in the safety zone.

Bizarrely, 12th-placed Swansea City, who this week announced that Real Madrid midfielder Luka Modric has bought a share of the Welsh club, could mathematically go up or down, as could Norwich City and Sheffield Wednesday.

SIMPLE EQUATION

Calculators might be required over the coming days but for Daniel Farke's Leeds and Scott Parker's Burnley, the equation is relatively simple. Eight points from their last four games would seal promotion with seven almost certainly enough.

Burnley, unbeaten in 29 league games, travel to 11th-placed Watford on Friday and if they win that could then guarantee promotion by beating Sheffield United at home on Monday. Leeds visit Oxford United on Friday and host Stoke City on Monday.

"This is about staying very level, very focused, not getting involved in the emotions of this time of year," Burnley manager Parker told the BBC. "My message is to stay calm. There's four games left, let's keep chalking them off."

Fourth-placed Sunderland are guaranteed a playoff spot but below them everything is up for grabs.

Bristol City, who host Sunderland on Friday, are fifth with 64 points, while sixth-placed Coventry, who lost in the playoff final two years ago, face a crunch Midlands clash at home to West Bromwich Albion, who are seventh and start the weekend three points below the playoff places.

Eighth-placed Middlesbrough and Millwall in ninth are also three points off the playoff spots and know that a bumper Easter could put them right in the mix.

Michael Carrick's Middlesbrough are at home to Plymouth on Friday before going to Sheffield Wednesday on Monday.

"It's four games, a mini-season. We've been higher in the league at times, we've been lower in the league at times. It's about now. That's what counts," he said.

"The picture after Monday will be a lot clearer."

(Reporting by Martyn Herman; Editing by Ken Ferris)