I spotted this in a book of letters by poet John Betjeman.  It is to the BBC Accounts Department on 26 Feb 1959:

"I am sorry you have had so much trouble to get me.  I delayed agreeing a fee until I knew how much work was involved.  This is now completed.  It involved reciting four of my poems, visiting different parts of London one afternoon with Ken Russell, spending a morning at Aldersgate here, being filmed and speaking an introduction into the microphone.  Spending an afternoon at King's Cross an Vauxhall Park, being filmed and speaking. Spending a morning going to Hatfield and being filmed there.  Going to Ealing to record.  And going another afternoon to Vauxhall Park and Finchley.  As a self-employed person my time is my chief expense.  Do you really think forty guineas is enough for what represents a good half-week's work?  I do not wish to be demanding and embarrass the promoters of what I think is an interesting experiment. But if there is any money to spare I wouldn't say no to some of it".

The source is John Betjeman Letters Volume Two: 1951-1984 edited by Candida Lycett Green.  The editor notes "JB finally agreed on fifty guineas for his part in the Monitor programme for BBC television which was called  A Poet in London".

I've updated the site with this.