It is one of the smallest commissions an artist can get - and does not even include their name.

But Cley lino cutter Robert Gillmor has thoroughly enjoyed his stamp duty, designing a host of first-day covers in the last two years for the Royal Mail.

Having debuted with bright lino-prints of his favourite subject, birds, he has three more sets of stamps coming out in 2012 - six sheep breeds in February, six pigs in April and six different cattle breeds in September.

The stamps, which are sought after by keen philatelists, are available in Royal Mail's growing number of pay-and-go machines.

But, with first-day covers still so popular, Royal Mail will not allow 75-year-old Mr Gillmor to show off his latest creations until they are on sale.

When he received his first UK stamp commission in 2010, Mr Gillmor had previous experience, having designed a set of stamps for the Seychelles in the 1970s.

He said: 'The Royal Mail has an official designer called Kate Stephens who has done several stamps. They decided they wanted to do birds, and found some work of mine in the web page of a gallery I work with.

'They invited me to submit some designs. Originally they were thinking of two sets of six garden birds and were going to go to photographs after that.

'But they seemed to like what I was doing, and I did all four sets of six for the birds. And I am now working on three sets of livestock breeds.'

He added: 'I found it very interesting work because I don't usually work on such a small scale. Apparently they have been very popular and two lots of the bird stamps have sold out.

'But I have declined doing any more stamps after the farm animals because they have taken up a huge amount of time and the deadlines have been strict.

'I need to get back to my ordinary work. The galleries that I supply have been very patient, but their patience could run out.'

Mr Gillmor said the stipulations from Royal Mail for the stamps included 'leaving enough space in the corner for the Queen's head'.

He added; 'The brief was for a single bird on each stamp, but I said they couldn't have a single magpie because of the saying 'one for sorrow, two for joy'.'

Each piece of artwork is a labour of love.

Mr Gillmor does painstaking research on the subject, then has to hand-cut and print at least seven separate linos for each final image.

He is helped by his old faithful printing machine, an 1860 Albion press that takes up a corner of his studio.

Much of the rest of the home he shares with wife Susan has its walls lined with bookcases full of tomes about birds. One shelf, containing more than 200 books, is dedicated to publications that have included examples of Mr Gillmor's work.

Mr Gillmor, who moved from Reading to Cley 14 years ago, spent 40 years doing illustrations for book jackets and magazines, including scores of covers for Collins New Naturalist series.

The sheer volume of his work means that most people will recognise his style, even if not his name.