According to HMRC, 30,750 operators of taxable machines have registered to date, and of those, 27,500 are pubs and clubs.
The tax went live on 1 February, and in March, HMRC officials said it would take a “sympathetic approach” to those who had not yet registered.
However, it has since warned that penalties may be due for those who have still yet to have registered, adding that “the longer people leave it, the more likely it is that a penalty will be issued”.
HMRC added that penalties may be between 30% to 100% of the tax due for the unregistered period.
An HMRC spokesman said: “It is important that HMRC provides a level playing field for all operators of gaming machines. We have guidance available, for all those who have registered, to understand their responsibilities, as well as guidance for those unsure if they need to register.
“We are conducting exercises to identify and help people who ought to be registered, but who are not yet registered.”
The spokesman added: “Penalties may be due if people register late for MGD, and the longer people leave it, the more likely it is that a penalty will be issued. However, HMRC recognises that this is a new tax for all operators of machines and HMRC will exercise discretion in cases where the law allows us to do so.”