That seems an odd way of looking at it. Surely if you are managing or designing a project and know that police / safer neighbourhood won't have resources (or indeed inclination) to police it and your own resources for monitoring are insufficient, it is the project manager's responsibility to design out problems. For instance, simply moving the gate to the other side of Herne place would solve the motorbikes in the park issue and practically deliver the same Railton LTN in every regard. I don't think many project designers of any sort would have the luxury of creating a hazard and arguing that because that hazard constitutes a criminal offence it should fall to someone else to rectify.
Re covering number plates, enforcement has to be central to the scheme. Of course it is not the scheme's fault that people choose to break the law. But it is very foreseeable that they will and that this creates a potential hazard. A plan should have been in place for how to deal with this, even if it is for instance a dedicated roaming LTN monitoring role, perhaps even shared with another borough. Or funding for an additional officer, or even shared officer, in the department which monitors such things. I'm not being specific - there are lots of options for various budgets. What is very disappointing is the apparent lack of preparation and assumption that someone else will deal with it.
I'm talking about the numberplate issue really - if the Herne Place motorbike issue could be resolved through design changes then yes that should be for Lambeth to deal with.
However, the issue of covered/fake numberplates is a wider one that Lambeth have little power to do anything about directly, because it has to be enforced by the police and yes that relies on police resources which in turn rely on political incentives to properly resource the police so that they can take action on this and a whole load of other things like speeding and dangerous driving in general.
People like me see that wider issue as one resulting from a general societal atittude that doesn't want drivers' freedoms restricted, but also hope that these attitudes are gradually changing, at least in London. Things can very slowly change if more and more people make a fuss about them, sufficient to make them an issue when GLA or westminster elections come around, because those are the bodies which decide how the police is resourced and what they should concentrate on.
Therefore - I'd prefer LTNs implemented in the knowledge that there will be some contraventions that people get away with under the current regime, than that they are not implemented at all. The number of people willing to risk doing things like covering numberplates is relatively limited and the number of people passing through the filters/gates will still be substantially reduced.
I would imagine this is effectively the view that Lambeth have taken - they know some people will break the rules and get away with it, but it won't render the schemes ineffective. I'm not sure exactly what they can do, really. As I understand it, local authorities are not allowed to take any revenue from speed cameras (it must go to central government) therefore they are unwilling to pay for them - would the same apply to cameras that could record numberplates being covered? If Lambeth were unable to reclaim any of the cost of running such things through fines then I can see why they would be reluctant to implement it. I am ready to be better informed on the technicalities of this, however.
The reason I suggest hassling the safer neighbourhoods team about it is that even if they have limited resources, they will tend to apply them where they think there's demand for them. I know that they get requests for dealing with various things that I'd consider less important than covered numberplates being regarded as a low risk activity, and they do go and deal with those things or at least give the impression of making an effort. Maybe even a sporadic enforcement action around LTN filters is outside of their scope or outside of what they can request assistance with from the wider met police... I don't know. I do know that sufficient numbers of residents complaining about speeding in specific locations can produce the occasional speeding enforcement.
Going back to what Lambeth can do via design measures - well, I'd be interested to know if the design of filter locations can affect driver behaviour to some extent. The one at Van Gogh Walk was mentioned upthread and this is one of the most successful examples of such a thing that I've seen. It somehow remains well maintained, and well used. I pass through it from time to time and there are very often people using it, whether it's kids kicking balls around, people sitting chatting or reading or having small scale barbecues. Driving past some temporary planters and a bunch of signage, hoping you'll get away with it is one thing - driving through a more extensive street redesign with a meandering route, and people around watching you, is another. Would it affect the behaviour of the fake/covered numberplate crew? I don't know but it might.