The reporting of this has been somewhat misleading, because it suggests that these are new offences, but in fact things like following someone, wolf whistling, catcalling and persistent staring are already illegal under the Public Order Act. What is being proposed is making it a specific crime, if these behaviors are done for a particular reason. The motive is the most important thing, rather than the behaviour, although you would need to have both to be convicted. 

It is rather like the way that an offence such as assault, becomes more serious if it is racially motivated. None of the behaviours mentioned above are defined in law, but they all come under the definition of threatening behavior. There is no time limit on how long you have to stare at someone, in order for it to become 'persistent staring', for example. It is very much in the subjective opinion of the person being stared at. If you stared at them for 10 seconds and they felt threatened by that, then it would be threatening behaviour. 

But there is a defence, which is that the person doing the behaviour must intend to cause a threat and that is where most of these things would fall down. Most wolf whistling is not intended to make the person on the receiving end feel under threat. It also has to make the person think immediate violence is about to be used against them. So cat calling someone from 100 yards away is unlikely to led to immediate violence and will not be affected.

Add to that the biggest problem, which is that most women don't bother to report these things anyway and I don't see that it will make much difference out on the streets.