There's no planning application such as the one you describe available to view on Lewisham's web site at the moment.

What makes you think that you'll be compelled to give them access to/via your garden, or that you'll not be able to use your garden while the works are in progress?

I can't imagine that a developer would constrain themselves with a requirement to access/use someone else's land, when that someone is likely to be hostile or an objector.

It's your garden, not theirs.