Amazing how this rambling rose has become so vigorous in such a small pot. And this photo was taken after I gave it a hard prune to reduce its size by about 50%.   

 David Austin has this to say about choosing a pot for a climbing or rambling rose: 

 "It must be large enough to accommodate an extensive root system, support a tall framework, and retain moisture without becoming waterlogged. Choose a container that measures at least 60cm (2ft) wide and deep, holding a minimum of 100 litres of compost".

 Good advice which doesn't seem to apply to this particular rose!