Manchester United qualified for last season's Champions League after winning the 2016-17 Europa League (they finished sixth in the Premier League that season)

The top four teams in the Premier League qualify for the Champions League, while the FA Cup winners, the Carabao Cup winners and the fifth-placed side in the top flight go into the Europa League. Simple, right?

If only.

At BBC Sport we get plenty of messages asking us 'what happens if this happens?' To be honest, we did not know all the answers until recently - but after delving deep into Uefa regulations, we have worked it all out.

So here we go...

Who qualifies for Europe normally?

The top four sides in the Premier League qualify for the Champions League group stages - usually (more on that later).

The FA Cup winners and the league's fifth-placed side go into the Europa League groups, with the Carabao Cup winners entering the second qualifying round.

However, it is often complicated by the FA Cup and/or Carabao Cup winners qualifying for Europe through the league. This season Manchester City have won the latter already - meaning sixth place in the Premier League now gets a Europa League spot.

Things are confused further by the fact the Champions League and Europa League winners get an automatic place in the following season's Champions League group stages.

Does it matter who wins the FA Cup?

If Watford beat Manchester City in the FA Cup final, then they qualify for the Europa League no matter what happens elsewhere. But if City win, then seventh place in the Premier League - which will be Wolves - gets that spot.

Until 2015 teams could qualify for Europe by losing the FA Cup final if the winners had booked a Champions League place. Stoke and Hull took advantage of the old rule before it was changed. But you now need to win the final to qualify.

If Watford do win the cup, then the sixth-placed team in the Premier League has to enter the Europa League qualifiers on 25 July. Manchester United, who are currently sixth, have a pre-season game with Tottenham in China on that day.

What effect does an English team winning the Champions League have?

Tottenham and Liverpool are in the Champions League final, and - barring an extremely unlikely set of scorelines to drop Spurs down to fifth on the final day - will already have qualified for next season's competition through league position.

That means the 'extra' group stage spot set aside for the Champions League winners would go to the Austrian champions, who otherwise need to go through qualifying as Uefa's 11th-ranked league.

If an English team won the Champions League and finished outside the Premier League's top four then five English teams would go into next season's group stage.

Uefa changed the rules for qualification last year - starting with this season's tournaments.

In 2012 Tottenham finished fourth but missed out because Chelsea won the Champions League and finished outside the top four - but Spurs would have qualified under the current rules.

Until 2005, Champions League winners did not qualify automatically - a rule which was changed when Liverpool won the tournament but did not finish in the top four.

There is no Champions League spot for the beaten finalists in the event the winners already had a place through their domestic league. So, for example, Liverpool would not have qualified for this year's competition had they not finished in the 2017-18 top four.

What effect does an English team winning the Europa League have?

Arsenal and Chelsea are in the Europa League final and the winners will qualify for next season's Champions League group stages.

If the winners finish outside the top four in the Premier League (which is almost certainly the case for Arsenal), it will mean five English teams will be in the Champions League.

However if they do finish in the top four (as Chelsea have), then England will not get an extra spot. The team who finish third in the fifth-ranked league - France - will go into the Champions League group stages instead of the qualifiers.

Even if the winners have already qualified for the Champions League through league position, however, there is no spot for the beaten finalists.

What happens when English teams win both?

There can be a maximum of five teams from one country in the Champions League. So that causes a bit of a mess if English teams win both European competitions but neither finish in the top four.

Obviously that won't now be the case this season, with Liverpool and Chelsea guaranteed top-four spots - and Tottenham and Arsenal battling for another.

If, in the future, the two tournament winners are both English and both finish outside the top four - but in a Europa League qualification place through the league, FA Cup or Carabao Cup - then the Premier League's fourth-placed team would not qualify for the Champions League and would instead drop into the Europa League group stages.

There would only be two Europa League spots - for the team who finish fourth in the Premier League and whichever other qualifier had not won one of the European tournaments.

If a season ever occurred when English teams won the Champions League and Europa League and neither of them qualified for Europe at all through domestic football - there would be NINE Premier League teams in Europe (five in the Champions League and four in the Europa League).

If one of them qualified for Europe and the other did not, then there would be five teams in the Champions League and three in the Europa League.

Got all that? We're off for a lie down.