Hello Cousin Alice – I am unaware of a Wm. Brewster Library and/or museum in London. I do know there is the American Museum of the Pilgrims in Leiden, The Netherlands if your travels allow time to get there. I recently learned that the founded passed away not too long ago,so I’m not sure of the status of the place. But here’s a link to it. https://leidenamericanpilgrimmuseum.org/en It’s located in a modest home built in the 1400s in the center of town. As for the London place, by best suggestion is to be in touch with British Pilgrim genealogist and historian, Sue Allan. Her e-mail is admin@mayflowermaid.com. I wish you well on your journey.