I personally loved Glasgow. You can sometimes get a return train from Liverpool really cheap, and there are some nice and cheap B&Bs in Glasgow. I recommend the Kelvingrove area. Just gorgeous.
Eurostar to Paris is a nice idea if you manage to book a cheap train. But every time I've looked it's always been too expensive for a return for me, especially since that is from London and you'd also need to pay to get to London too and back. Also accommodations is super expensive in Paris. :/