National League clubs have been warned they will be relegated if they choose their 3G pitches over promotion to the English Football League (EFL).

As it stands Bromley, Maidstone United and Sutton United are the only three clubs operating in the non-league top flight with artificial surfaces.

But last year Chester FC chief executive Mark Maguire said the club was exploring the possibility of installing a 3G pitch and, given the additional revenues streams the surfaces can bring, it could be an avenue further clubs go down in the future.

The National League allowed teams to play on 3G pitches for the first time last season.

However, as Press Association Sport today reports , the league asked clubs to sign an 'irrevocable undertaking' that they would be willing to rip up their 3G pitches if they won promotion to League Two - or face relegation to the sixth tier.

That is because artificial surfaces in the EFL are not allowed.

The scenario could yet play out this season with Sutton sitting third in the table and Bromley one point outside of the play-offs in ninth. Maidstone are seven points adrift in 13th.

And National League chief executive Michael Tattersall, speaking to Press Association Sport , said: "If we don't send the EFL two eligible clubs they will reprieve the 91st club and we will have undermined our raison d'etre.

"I don't want to relegate a club on this basis - nobody wants to do that.

"But the irrevocable undertaking was not a work of fiction.

"You have to mean it and if you fail to live up to it we're not just going to tickle your tummy.

"It sounds draconian but it's necessary. Should we hold a play-off final if one team isn't going to accept promotion? (The relegation rule) is the least bad solution."

Sutton, Bromley and Maidstone wrote to the EFL in August calling on the league to 'show leadership' by making 3G pitches legal.

EFL chief executive Shaun Harvey said in December that the potential use of 'synthetic or artificial grass surfaces' would be discussed as part of an ongoing review of stadium criteria.

But he noted that any rule change would need the backing of the majority of EFL clubs at the league's AGM in June and would not come into force until the 2019-20 season.