According to a Freedom of Information request, made by the Pubs Advisory Service (PAS), PCA Paul Newby has been subject to 12 challenges by pub licensees, of which four were upheld.
A spokesperson for CIArb told The Telegraph in December that a challenge would be permitted against the group's members, of which PCA Paul Newby is one, if “circumstances exist that give rise to justifiable doubts as to the arbitrator’s impartiality or independence”.
The spokesperson added that a successful challenge didn’t necessarily mean that the wrong decision had been made by the arbitrator, but that when a challenge was upheld, an arbitrator’s appointment in that individual dispute is “immediately terminated”.
However, a spokesman for the PCA said given that its responsibilities had been established by an act of parliament, it did “not accept that the Chartered Institute of Arbitrators has any jurisdiction to appoint or remove an individual from the role of arbitrator in a pubs code arbitration”.
"Paul Newby is determined to maintain the independence of the PCA in carrying out his role as parliament intended and continues to act as arbitrator in those cases that have been challenged and where the challenge has been upheld by the CIArb," they said.
In the letter, chairman of the BPC, and former MP, Greg Mulholland, said: "This is extraordinary – and even considering the woeful performance of Mr Newby since he took the role – is a new low.
"Mr Newby has faced calls to step down ever since he was appointed in March 2015 over financial connections he retains with Fleurets, a company that makes 20% of its turnover from large pubcos – that the pubs code adjudicator is supposed to regulate.
"Mr Newby failed to properly declare that he had intended to retain (and still retains) both a 10% share in the company and has a loan to Fleurets owed to him with an initial value of £350,000."
The letter urges the BEIS committee to take up the matter as a matter of "some urgency" and hopes it will write to Greg Clark MP to raise the matter in the House of Commons.
"The legislation that parliament voted for is being undermined, flouted and corrupted, and this is an insult to parliament," the letter read.
"Paul Newby has demonstrated beyond any reasonable doubt that he is not only wholly unsuitable to be pubs code adjudicator, but worse still is undermining the very statutory code he is supposed to uphold.
"He must be sacked and an impartial and principled pubs code adjudicator appointed who will actually carry out this hugely important statutory role in a way that will deliver the principles of the legislation passed by parliament."
In October last year, Reeves wrote to the PCA with concerns emphasising that his office is under scrutiny and that campaigners have raised serious concerns about tied tenants' access to the market-rent-only option (MRO), which is dealt with under the pubs code.
The Morning Advertiser has contacted the PCA for a comment but has not yet had a reply.