It all depends what you say to them on the phone. If you dial 999, categorically state that you are in fear, that you have received threats of violence directed personally at you and that you require immeidate assistance, you do not have any assistance on site, and that you are a referee with 20 plus people being involved potentially against you, then you'll get bumped up the queue, fast.
If you dial 101 and just say that some guy said he wanted to punch you, but he's being talked to by his mates, no immediate threa etc they'll get back to you for a statement in a couple of days.
it's how you sell the situation to them that dicates their response. But to help you out, know the location of your park / pitch / ground, siginifact land marks around you if unsure of address etc.
No matter how bad it gets, there will always be one person there who you can ask for assistance. I've found that say it's Red Nr 6 that's the problem, speak to the opposing team's either captain, or Keeper. Captain as you would think that they can be that one step above all of this, or keeper as he's a) at the other end of the pitch, and b) it's not his mate that's gone off on one. Make you way over to them, or gesure them over to a neutral spot and ask for their assistance / tell them that you are abandoning and walk with me to the club house / car ya de ya.
This person then also becomes you nr 1 witness,as they have been with you and should ave heard everything you heard from your point of view / location / distance.