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One of the most important factors affecting value for many items going to auction is the maker. This is particularly true when it comes to fine art, whether drawings, prints, paintings or sculpture.

It can be quite hard to get your head around how this works with conceptual art – an idea conceived by an artist but actually executed by their assistants, without them having a hand in its manufacture. Certainly, with Old Master portraits, many of which were completed by studio assistants, it is only when we know that the most important parts – usually the face and hands – were painted by the master himself that we can call it an autograph work and the price shoots up. This is why catalogue descriptions can range from ‘attributed to’ all the way down to ‘Circle of’, ‘School of’ or ‘Follower of’.

The magical hand of the artist has made all the difference to the star of this year’s Royal Academy Summer Show Keep Ou. Another comment on Brexit by the mysterious Banksy, he has used as his ‘canvas’ an arrivals gate from Terminal One, Heathrow, sold off last year as surplus to requirements. I have no idea what the price was when the hammer fell then, but you can bet that the RA price tag is considerably higher.