Our rear extension, proximity to neighbour's conservatory

Sinam123

Hello,
We are in a semi-detached house built in the 1980s, and we have a conservatory in the rear that we are planning to bring down to build a proper extension in its place. We are planning to do it under Permitted development regulations ( under 3m).
Our neighbours also have a conservatory right next to ours (about 1m distance between our conservatory and their conservatory).
We have kept our neighbours informed of the extension.

Now, for our rear extension we obviously need to dig foundations. We are planning to dig 1m foundation. Reading the requirements to serve Party Wall notice, it looks like we have to serve the notice if we are excavating within 3m and the foundations are deeper than the neighbour's foundations.
I believe our neighbour's main house building has 1m deep foundations. But I am not sure of the depth of the foundations in their conservatory.
But do we have to consider the conservatory's foundations in this calculations?
Or as long as we keep to the 1m depth (which is also their main house's foundation depth), are we ok?

Thanks

Doozergirl

You need to consider their conservatory.