Buying Home on Greenbelt - HELP!

[KTTKTK]

We’ve just had an offer accepted on a chalet-style semi-detached home in Lemsford Village
We had hoped to make it our forever family home. the current footprint is a too small for our needs, but the has substantial land-plot -I hoped to immediately starts works on a 2storey wraparound extension

However, I tracked down the seller’s architect who had visited the property, who shared some limiting details:

• Home is on Green Belt land
• Home is also on a Conservation Area
• Has an existing extension in 1980 (side extension and rear extension 2.6m deep) - from the greenbelt 50% volume rule, this property is approx. 75% over the original footprint

Naturally, we’re saddened — but we’d love a second opinion before making a decision to proceed or walk away.

Is it very unlikely that we should walk away? we're really struggling to find house as we keep losing bidding wars to insane developers

I've Attached:

• Photo of Front & Back of Property (alongside back of attached neighbouring home)
• Site Plan (highlighted in red)
• Existing Floor Plan
• Proposed Extension Sketch 1 (rough sketch of 2Storey wrap-around)

I think I’d consult with a planner and get some advice on either going for pre-planning or submitting a formal application to get the same as next door. That shows that a clear precedent has been set and the style is much more sympathetic to the style of the house, so you’d have a decent chance, especially if not a conservation area. I also think you could do the same sort of thing but much better given that techniques have moved on since the 1980s so you’d have a nicer house at the end of it.

Also to state the obvious, if you’ve not had much luck, your budget is a bit tight, you like where it is and you’d be happy there, even if it’s not perfect it’s ticking quite a few boxes isn’t it?

Also if you had to re-do some of the extension but did it double height, chances are you’d not breach the footprint rule either. I’d have thought that both your house and next doors’ footprint were exactly the same originally.

To be honest OP I think you would ruin this gorgeous house by extending it so much.
If you need a gigantic house could you not either buy one or build from scratch?

Thanks evryone for you hones I really appreciate it!
Before I pull out of the sale I am tempering my expectations focusing on a Permitted Development (PD) route
To Reterate:

• on Green Belt (not a conservation area)
• existing extensions in 1980 ioncreases volumbe by 70% (side extension and rear extension)
• semi-detatched

My Proposed plan to justify sale:

(see image 'proposed floorplan' attached)

1. Ground Floor Rear Extension (6m deep)

• Demolish existing 2.7m rear extension
• Rebuild a 6m deep rear extension via Prior Approval (under Class A.1(ea))
• There is an existing boundary wall marking 6m deep (see image)- litle/no loss of light for neighbour

1. First Floor Rear Extension (3m deep)

• Extend 3m from the original rear wall, (under Class A.1(j))
• Leave 2m boundary gap retained from the attached neighbour property
• Only extend 3m (Not 6m) to comply with PD
• will still be behind neightbour's boundary (see image)- litle/no loss of light for neighbour

I spoke with one of the Council's planning duty officer

• council cannot look/discuss plans unless I have professional drawn plans and pay for pre-planning. At this stage I hesistant to pay for an Architect if I am unsure going through with sale

• council advised that within Permitted Development I can either: Do ground floor 6m deep extension OR a 2storey 3m deep extension - I cannot extend 6m and 3m

Is there any arguments to be made for a planning like this (see image 'proposed floorplan') to go forward?