I think you forgot to say which abrsm grade you are currently at, Jon, though in any case I don't know exactly how they compare. So unless someone with experience of both the abrsm and Delcamp grading systems can offer an opinion, your best approach is probably to look through the lessons of the course that is just finishing and see which seem most useful to you, then apply for that in September when the new session starts. You might like to start working through some of them privately in the meantime, then you can keep your options open and will have a better idea when September comes. When you do register, it isn't for any specific level, so If you start one and find it is not appropriate, you can change to another level, though you would need to go back to the first lesson in that new level and catch up from there. You could register to start the lessons now, if you wished to participate actively rather than follow them privately, but bear in mind that at this late stage of the current course there will not be very many other students about to exchange feedback with.
Classical Guitar Forum.
"Experience is something you don't get until just after you need it." - Steven Wright