I'm not so sure about that. I've seen people convicted on quite flimsy evidence, simply because magistrates are unwilling to go against the word of a police officer.
My guess is that if punters are criminalised, simply being seen visiting a known prostitute will be sufficient to get a conviction. The argument that the suspect knows the girl and vice versa won't hold any water. All they have to do is catch you coming out of her place, or even worse her leaving your place. I can imagine them having a field day staking out an incall girls place with video and arresting every guy that emerges. They'd even be able to prevent them warning her by intercepting out of sight and carrying out an immediate arrest.
I'm not convinced. If you look at 'recreational' drugs as an example, you have to be pretty fucking unlucky or stupid to get busted, or be a major dealer. The only people I know of who have been caught are generally either smoking dope in public, or caught by dogs & searches at festivals/clubs. If the police wanted to, it would be possible to catch dealers by discreetly following everyone who has ever been busted around until they buy again. Then follow every dealer around until they go to their distributor etc. They don't do that though, because they have neither the inclination nor the resources.
As for court, as usual, it will depend on your ability to pay for a good lawyer. If you can't afford one, you'll get done, if you can, you'll be probably ok.
So as with most matters, those with plenty of cash to pay for outcalls, own hotels, lawyer if they get caught will be unaffected, whereas people with less money to punt with and defend themselves will get stung.
Even the people campaigning for this change quietly admit it's impossible to enforce 100% They see it more as a symbolic thing "showing that's it's unacceptable for men to buy women" to make it illegal. Yeah, like drugs being illegal makes users think they're wrong.
That Newsnight debate really showed the Anti's true colours. Their line against Laura Lee was "yeah, you and a bunch of others might enjoy sex work, but our made up statistics show the majority don't, and you legislate for the majority, not the minority."
So basically, screw minority interests and individual liberty, you're in the way of our social engineering plans.