Female visitors to London are unlikely to have many problems, provided they take the usual big-city precautions. Don’t get into an Underground carriage with no one else in it or with just one or two men. And if you feel unsafe, you should take a taxi or licensed minicab.
Apart from the occasional wolf whistle and unwelcome body contact on the tube, women will find male Londoners reasonably enlightened. Going into pubs alone may not always be a comfortable experience, though it is in no way out of the ordinary.