OK - to be very clear: the distance from the original rear wall of the dwelling (the rear wall of the outrigger), to the rear most point of the rear-most proposed extension is 3m.
So if we follow our plan, the original outrigger will remain intact since it is only the old 3m extension that we will be rebuilding. Promise!Oh right. In that case, one more complication might be that through demolishing the original outrigger to then rebuild and extend it, the council may well take the measurement from the rearmost wall you are not demolishing as in effect you are building a 6m extension (albeit you refer to part of the extension as a re-build).
Not sure you will get much more useful advice on here, you may be at the point of having to decide whether to seek the Council's view (i.e. apply for an LDC), or wing it.
With full planning I would be willing to place a bet that they would not allow the 3m extension that is infilling the gap. At least they would not allow it unless I lowered the whole thing to fence height (around 2m) and then dug down. I had a look through old planning applications and they were pretty much rejecting all rear extensions on terraced houses due to amenity of neighbours.and if you get full planning, you can choose to demolish it or just add on, and nobody can complain...
This is my last attempt (!). If you demolish the old 3 metre extension, then rebuild that, plus 3 metres, it will considered as a 6m extension.
I'm going to have to withdraw from proceedings as I can't make it any clearer
lt8 - It isn't written anywhere in the PD rules regarding the "Gap" it's come from precedent and it would probably apply everywhere (single storey / 2 storey / side / rear etc.)
I.E. If you have a side wrap around extension and want to put a rear extension immediately next to it, if the extension "reads" as one then even if it is separated by a few millimetres, it's likely to be judged as one big extension (especially so If it has clearly been built to function as one large extension). Tony's last post puts it across well.