I have a large paperweight similar to this, although mine has a slight neck on top of the dome and a knob on top of the neck. I have been told by a Canadian collector who should know - a glass expert originally from England - that these are an interesting and unusual Whitefriars design and manufacture, and are considered "doorstops." They are larger than usual paperweight-style items.
There are slopping rounded versions of the doorstop design as well as more specifically doorstop-looking versions (as pictured below). There is also the version you have, without the neck and the knob, which looks more like a traditional paperweight. They were all made sometime in the 1970s according to the glass expert. They are an unusual and highly collectible design from a glassmaker that generally made millefiori paperweights.
If you click on the link below and scroll down, you will see something similar to what you have.http://www.circaglass.co.uk/phdi/p2.nsf/supppages/circa?opendocument&part=3