I think they should do fine. If you think it'll be chilly (London - Hamburg seems like it could definitely be a bit cold and rainy) you may want to consider thick merino wool socks. Because of the fabric they wont feel like an oven even in warmer temperatures but will keep your feet comfortable if it gets colder.
I would just put the overshoes on when it's needed, but that really is a matter of personal preference.
I think they should do fine. If you think it'll be chilly (London - Hamburg seems like it could definitely be a bit cold and rainy) you may want to consider thick merino wool socks. Because of the fabric they wont feel like an oven even in warmer temperatures but will keep your feet comfortable if it gets colder.
I would just put the overshoes on when it's needed, but that really is a matter of personal preference.