It's quite common unfortunately. Pest Control Office are a more serious problem than many realise. A cancer to the market.
The artist isn't going to do anything re PC so the only option is solicitors letters and people speaking out publicly(nobody wants to do this but they're left with no choice).
Or wait until PC is shut down, then the coas will be useless and normal practice of due diligence will resume. Might be a while.
As it stands, without a coa not many will risk buying.

 That's not true unfortunately, works have been sent to auction in that hope and not received a coa. I know you mean well but the last thing the market needs is encouragement for more works to be sent to auction. Actually the last thing the market needs is the current Pest Control.

 And yet Pest Control advise anyone interested in buying Banksy to use the Check before you buy section on their website, sharing all info including unredacted coas. Meaning the seller must share this info with prospective buyers first. Collectors shouldn't do this. Unscrupulous individuals will have everything they need without spending a penny to create exact fakes.
The right thing to do would be for the seller to share this info with PC along with the prospective buyers contact details. At that point PC can liaise with the buyer to confirm it's authenticity. 
Anyone could contact a seller on the forum/gallery and offer asking price, request the required info to confirm with PC, as advised on their website. Take the info, disappear and create 10 fakes. If they were smart they would reach out to all galleries and private sellers, collect as many images as possible and sell volume quickly at very tempting prices in a short timescale. A flood of fakes before PC know what's going on.
Rule 1- do not share unredacted coas(cover serial number). The only people that should have this info is PC and the current owner. It's no use to anyone else other than forgers.
Rule 1 is the reason the concept of the coa worked so well.
Although if they don't reply in a timely fashion the whole concepts useless including the coa as people can't wait for an unknown timescale to sell their art.

When challenged PCs reply was-we would spot a fake a mile off..
Yeah maybe, but by then it will be too late for the people who bought the fakes. PC sure as hell aren't going to help people with fakes whether they bought them unknowingly or not. This isn't market control or looking after the collectors. This is laziness. It's simply them trying to make their lives as easy as possible without any regard for others. 
 


The systems broken, they need to fix it.

If you read the terms and conditions I think the OP will struggle:
pestcontroloffice.com/terms.asp
The only argument would be that the terms breach consumer law and shouldn't stand. I highly doubt anyone will succeed in making a claim against PCO, they have really good lawyers behind them, one of whom I'd say is heavily invested in brand Banksy.

I suppose a claimant could say there's been some implied breach of contract due to delay however the terms clearly state that PCO are under no obligation to provide a certificate and it's within their sole discretion if one is issued. You could argue negligence however one of the limits of their liabilities prevent any claim under torte, plus if they haven't issued a decision on authenticity I'm not sure they can found to be negligent. 

I'm in no way defending PCO, I think it's a shit show. I don't buy the argument that they get inundated with emails and can't cope, if that's the case charge more for the service and hire more staff, they should also charge a nominal non refundable fee for any submission (Say £10-20) to cut out twats trying to get posters authenticated. If the service was more expensive with a non refundable element it would discourage chancers and obviously provide sufficient resource to run properly. It's not rocket science, which raises a lot of questions as to why it's being run in this way. I don't think the courts will turn this round (they may if a few people with deep pockets all bring large claims at once, regardless of their merits), more likely public opinion and and press will push change. 

I hate to say it but I have used Pest Control multiple times over and whilst they have never been quick at getting the COAs out (the longest though was only 9 months) they were always very diligent at authentication which has been a god send.

I think they are probably backlogged with people trying authenticate things that COAs are not applicable for as the "real" volumes will have fallen significantly over the last 18 - 24 months. If you do want to sell however the Auction houses do have a fast track service with PC...but you may not get the best price with all art pricing and collectables in the doldrums due to lack of disposable income and therefore buyers/collectors.

It's coming up to three years for a couple of signed prints with full provenance here, granted one of them has a loveheart in place of a number, but with a letter from the artist it was gifted to for their charity auction and receipt I don't see the issue. I suspect the other is a DN, double number, but again, traced back to source and full prov. Informed the artist needs to physically see and ok them before a COA can be issued. This being administrated through one of the two largest auction houses in London so...