It is thought the pictures were taken at around 1.50am. Four young men in dark clothing and hats were seen running off towards The Green.
The stolen works, thought to be worth around £230,000, include a Henry Moore crayon, pen and ink sketch titled, Three Reclining Figures On Pedestals, an oil by Dorothea Sharp titled In the Lily Garden, with a painting called On the Sand Dune, also by Sharp, on the reverse, and Edward Seago's oil Thames Barges at Low Water, Pin Mill.
Simon Shore, co-owner of Trinity House, who will open a second gallery in Mayfair in November, said: "If there is an attempt to sell them on, these instantly recognisable paintings by well-known British artists will be worthless on the open market."
Anyone with information can contact West Mercia Police on 0300 333 3000, quoting 52S/060810, or call Crimestoppers anonymously on 0800 555 111.
• On the same night, two oil paintings were also stolen from a private home on Main Street, Wymondham, near Melton Mowbray in Leicestershire.
The incident happened between 7.15pm on August 5 and 12.15am on August 6, when the occupants returned to find the back door open.
The two paintings taken were Sportsman in landscape by the British artist William Nedham (d.1849), a 21in x 2ft 8in (53 x 81cm) oil on canvas of a bay horse in a landscape in a simple gilded frame, and a landscape oil of moorlands with ducks flying over a lake and cows in the foreground, and oak leaf decoration to the gilt frame.
Detective Constable Lee Fowler, the investigating officer, said: "We have spoken to members of the Wymondham community and to local art and antique dealers, but now we are appealing to the wider public.
"We would also like to appeal to art and antique dealers further afield who we haven't already spoken to. If you are approached by anyone trying to sell you the pictures then please call us immediately."
Anyone with any information is asked to contact DC 395 Lee Fowler on Leicester (0116) 222 2222, follow the instructions to leave a message for a police officer and when prompted key in the officer's identification number 0395. Alternatively contact Crimestoppers, anonymously, on 0800 555 111.
• Meanwhile in an unconnected development, two Hertfordshire women have set up a website where victims of theft can list their stolen items and anyone seeing something suspicious can check to see if the item is stolen.
Angela Jefferson and Carol Smith launched www.itsbeennicked.co.uk at the end of June with the insistence that all items listed must first be reported stolen to the local police and an incident number obtained. This is for the user's own safety as the site does not allow the publication of personal details.
Mrs Jefferson originally had the idea when she became fed up with thefts from the farm she ran with her husband.
She told ATG: "Once you have reported the theft you can upload a photo and a description of your missing item instantly. It can be on the website within minutes with no time wasted at all. Our local police have been very supportive and helpful with setting up the site."