If we separate Premier League players into two categories: English and non-English, we'd find that English players in total play a little over 30% of the minutes per season. It is a common belief that the number of foreign players is affecting the quality of English players that England produces.
Gerrard said it after the 2008 EURO, the sentiment was shared by Sir Alex Ferguson, Sepp Blatter, and Michel Platini. Greg Dyke, chairman of the English Football Association, said in 2013 that if things keep going this way, it is only a matter of time before the Premier League does not have enough English players to play for the national team.
It seems like an open and shut case, however.
The Real Problem
The English national team's problem isn't the number of players playing in the Premier League being not enough, but it is too high.
Here's the idea; The Premier League is the most competitive league in the world, so if you approach it with the idea of a local English League then yes, that 30% is too low.
However, you should approach it in the sense that every country in the world got together and decided to form the best football league in the world, one that would often be seen as more competitive than the UEFA Champions League, something I personally believe. When you approach it like that, then having 30% is actually a high percentage.
The problem isn't the percentage being too low, it is actually too high. English players benefitted the most from that as their 30% was playing intense games all season. English players now need extra effort to keep their place.
England would actually get hurt the most by any regulation reducing the number of foreign players because not only would it affect the popularity of the Premier League, but also reduce the effort English players need to keep their place. Even exceptional talents would be less motivated since they're keeping their place anyway.
How England Beniffited So far From That
If we look at 1995 as the year the Premier League was globalized as it had just been turned into its current Premier League form and also being the year that Bosman ruling was introduced in Europe, we'd find that England's win rate went up from 52% to 62% while also increasing the times England makes into advanced stages in the knockout stages.
The Problem Is The Number OF English Players Outside The Premier League
The intense and exhausting level in the Premier League often fails the English team in international tournaments. Thus, they need more players in top leagues outside who take the usual rest amount mid-season.
England's manager between 2001 and 2006 Sven-Göran Eriksson said that exhaustion was the main reason England got knocked out of the 2002 World Cup and 2004 Euro. Both tournaments saw England not scoring once in the second half.
Steven Gerrard echoed that statement. Lampard described the players as "dragging themselves across the pitch" in the second half. Fabio Capello said the same thing after the 2010 World Cup where again England didn't score once in the second half.
In Conclusion
The English Premier League has an interesting season, to say the least. Their most intense period is when other leagues are taking a break, replacing that with a winter break later in the season. Something is clearly not working in that system.
Meanwhile, they lack the number of players outside to enter the summer with the correct amount and timing of the rest. Players in top clubs in their league that wasn't playing for three titles locally and one in Europe.