That’s no more help from me then… I’m out
My advice is to take out the original switch. You won’t need it. And if you use it then you can’t use the smart functionality.
That should give you plenty of space…
Use the relay linked earlier where the current switch is and put a blank face plate to close it up.
Put the PIR where you want/need to, it’s hard to say where since we don’t see the room. Perhaps that is the same place as the relay, perhaps not.
Use a second Nodemcu/D1 mini/ESP board of some kind to read the PIR state (if needed).
Set up the automation between PIR and relay.
Buy a IKEA or Philips Hue remote and have this to manually flip the relay. (not sure about the IKEA remotes but Philips Hue will work if you have any Hue hub).
The only thing we did not clear here is the dimming. But that won’t work with a relay. And we would need to know what kind of lights you have in order to dim them correctly.
I use a Shelly flashed with ESPHOME with a mains PIR connected to the switch input, as well as the normal switch. When the switch is on, the light stays on (unless switched off with the app). When the switch is off, the PIR takes over.
Similar to this:
Phew! 
I was just revisiting your post several times to see where the help was. Nope - can’t find it 
Lighten up bud , it’s just fun and games - like all computing , don’t take too much to heart or seek out offence where none is intended. You’re only hear on this rock once, enjoy it, have fun, smile and wave your hands in the air when exasperated and think “oh well, good luck to them and all the best”. You might enjoy your time on planet earth that much more 
@Hellis81
Thank you for your sustained help, real valuable positive help, 
Never thought of that - simple indeed - and plenty of room. but read on…
Good idea. The switches are in hallways and/or ingress/egress areas of the house. So it doesn’t need to be super accurate , just when someone passes the switch so I could drill a hole and use a grommet to mount the PIR.
So to clear my ignorance on this, are you saying I would need 2x boards, a PIR, a 240v relay and a power supply, all behind the switch? I’m confused sorry.
Other notes:-
- The manual override (physical switch) is a must and keyfobs or remotes are no good for the application I need and the family. I’ve seen touch sensors that connect to ESPs, £4 , one just fixes a loop terminal to the screw holding the metal facia plate where the switch facia went. That will do.?
- Additionally, would I need to program anything and if so how do I send the code to the device(s). More equipment/costs? Apologies - this might be bread & butter to you but it is all new to me and I am sure there is a bewildering set of options and devices , this is where I need help , the programming I will be ok with as I am a programmer - but I am not a hardware engineer and not experienced in these areas. That is why I came here
No…
Let me clear the confusion. Option 1, you have everything in one place:
1 relay board as linked in the past
1 PIR
I’m honestly not sure if it needs a power supply or not. I looked at the pictures and couldn’t see anything that suggests it can take 230 volts to the input, only the switching side.
It should have some pin(s) left to use for the PIR. The realy should only use GND, VCC and one data pin.
Option 2, The PIR needs to sit in a different location.
1 relay board
1 PIR
1 ESP board of some kind
1 (or 2) power supplies/transformers/chargers
You will need to program the boards with a configuration using ESP-Home.
Most of the configuration can be copy pasted but you will need some tweaking I believe.
This is what I mean.
PHILIPS Hue Dimmer switch Smart Wireless LED Lighting Remote Control | eBay
You stick it on the wall with tape and the remote attaches to the plate with a magnet.
IKEA has a similar product, but I have never used one of those.
Having touch things like that will be harder and require more in the configuration/programming.
You could have a look at what @Holdestmade suggested too.
It’s not a bad idea. Probably less DIY involved.
Ooops @Holdestmade , I missed your post. Sorry. thanks for the info. I cannot put PIRs into the ceiling without major housework - out of the question. Had to google “Shelly” and found their latest 2.5 on sale for around £20. I still need PIR and blanking plates. Cost is becoming an issue with that solution. But then I found “Shelly 1” for around a tenner. Now we’re talking. So with a Shelly 1, a 240v inline PIR, and a plastic cover I am 90% there. Just need to figure out a means for manual override. Maybe a 240V 5A push-to-make switch mounted on the plate - need to check Part-P electric rules. A normal light switch will not leave enough space for a Shelly 1 behind it me thinks.
Yep done, missed his post 
Thank you with the ESP - I think the Shelly 1 or similar is more than enough. I saw SONOFF switches too, they don’t need a hub/could either with HA - correct?
Yes, I use Shelly 1 for some lights, Shelly Dimmer for others. Not tried Sonoff but they look similar and can run ESPHOME as well.
You could use one of these next to the existing light switch and put the Shelly 1 in the light fixture (or above it)
Not sure what your light fitting is like but if you have a standard ceiling rose, you can replace with these and they give plenty of room to fit the Shelly
https://www.amazon.co.uk/gp/product/B07GJNVT2K/ref=ppx_yo_dt_b_asin_title_o07_s00?ie=UTF8&psc=1
@Holdestmade - DAMN YOU - you STAR . That is PERFECT. A Shelly 1 (or SONOFF switch - the £8 simple ones) and this PIR. My god you’ve only gone and done it. 
EDIT:
Maybe the kiss was gratitude a tad too far 
Just found this, it has an override switch on it and doesnt need a neutral, not tried it though
https://www.tlc-direct.co.uk/Products/DNWAPIR.html
EDIT: crap just noticed its £50 !
Yeah, but £50+ OUCH 
Your previous suggestion was 100% on the money with free cigar 
don’t trip up whilst you’re on a roll 
@Holdestmade that’s more like it. Nice 1 thanks. I’m going to look into these PIR types and the shelly / sonoff combo.
@Hellis81 thankyou for all your kind help too