English clubs offer a professional contract a year ahead of French and Spanish clubs which they use to their full advantage with young players who have not yet signed with their parent clubs. It gives them a headstart in their scouting which Chelsea did with Gael Kakuta at Lens and Manchester United with Paul Pogba at Le Havre.
I think what enrages most clubs is that they invest so many hundreds of thousands of pounds in the training of the player only for him to be tapped with the promise of big wages and a starting place in a big foreign club. These under the radar negotiations happen because the buying club knows that there are usually no pre-contracts. The player leaves without the club ever getting any financial compensation.
To make sure that there is an even playing field, clubs could sign player bonds keeping them in the club for 5 years after their training. If a player breaks a bond the club can recoup the amount calculating a prorated amount for the years left in his bond period plus negotiate a fee from the buying club. It happens with financial companies who pay for executive MBAs and expect the employee to honour a three year commitment thereafter or pay out if they leave earlier.
Sounds draconian but with inflated transfer markets, each club with well regarded youth programs will need to do more to protect their assets. Conversely, such safeguards can spur English clubs to pay more attention to developing their own talent.