Land and Plots at Auction: Pricing the Planning Risk

Why Land Lots Are a Different Game

Most auction catalogues mix houses in with the odd plot, paddock or site with outline planning. Investors who are used to comparing a guide price against sold prices on the street often carry that same instinct into a land lot — and it fails completely. A house has comparables. A building plot doesn't sell for a price per square foot; it sells for whatever is left over once you've built and sold what the planning permission allows. Get that calculation wrong and a guide price that looks like a bargain can be a loss-maker before you've turned a spade of earth.

Of the 36 "Best Buy" lots our model currently flags (houses under £300k with estimated value at least 1.5x guide, average guide £102,785), the overwhelming majority are finished or near-finished houses — because a standard valuation model can price those against comparables. Land doesn't work that way, and that's exactly why it gets mispriced by buyers who skip the sums.

Residual Land Value: The Only Method That Works

The residual method starts from what the finished scheme is worth and works backwards to what the land should cost:

Residual land value = GDV − build costs − fees − contingency − finance costs − selling costs − required profit

Every term matters, and skipping any one of them is how people overpay.

Worked example

A 0.3-acre lot comes up with outline planning permission for three semi-detached houses. Guide price: £45,000.

• GDV (Gross Development Value): 3 units × £220,000 = £660,000
• Build cost: £140,000/unit including groundworks, services connections and external works = £420,000
• Professional fees (architect, structural engineer, building control, planning consultant — roughly 10% of build): £42,000
• Contingency (5% of build, land and plots deserve more than the 3-5% you'd use on a refurb): £21,000
• Finance costs (development finance over a 9-month build at ~8%, drawn down in stages): roughly £18,000
• Selling costs (agent fees + legals at ~2% of GDV): £13,200
• Required profit (20% of GDV — the minimum most lenders want to see before they'll fund it): £132,000

Total costs before land: £420,000 + £42,000 + £21,000 + £18,000 + £13,200 + £132,000 = £646,200

Residual land value: £660,000 − £646,200 = £13,800

The guide price is £45,000 — more than three times what the sums support. On paper this looks like a cheap plot next to £220,000 finished houses nearby. Run the residual calculation and it's actually overpriced, and bidding to anywhere near the guide would turn a viable scheme into a loss.

This is also why land often sells for less than its guide suggests it "should" — sophisticated bidders are running this sum in the room and simply won't go higher.

Planning Risk: What to Check Before You Bid

Outline planning is not full planning, and full planning is not a guarantee the scheme as costed will actually get built:

• Read the planning conditions in full, not just the decision notice headline. Conditions on materials, drainage, tree protection or archaeological surveys can add real cost before you lay a brick.
• Check for a Section 106 agreement or CIL (Community Infrastructure Levy) liability. These are direct cash costs, sometimes tens of thousands of pounds, and they're easy to miss if you only read the planning permission and not the associated legal agreements on the council's planning portal.
• Look at the local plan allocation, not just the existing permission. If the site sits outside the settlement boundary, a lapsed or unimplemented permission may be harder to renew than the auctioneer's marketing implies.
• Confirm access and easements. A landlocked plot relying on a right of way over a neighbour's land is a common trap — the legal pack should show the easement is registered and unconditional, not just "understood to exist."
• Check utilities capacity. A quote from the local water authority for a new sewer connection, or confirmation the electricity network has spare capacity, can be the difference between a workable scheme and a six-month delay waiting for reinforcement works.

The Legal Pack Still Matters — Differently

For land, the legal pack needs a different read than it does for a house. Look specifically for the planning decision notice and all attached conditions, any Section 106 or CIL documentation, evidence of registered easements for access and services, and a plan showing the site boundary matches what's being sold — un-registered or partially registered land is common with plots split off larger holdings, and boundary disputes are expensive to unwind after completion.

Financing a Plot Purchase

Standard bridging works for the land purchase itself, but you'll need a separate development finance facility for the build, and most lenders want to see planning permission (not just outline) and a fixed-price build contract before they'll commit. Read auction finance basics before bidding — arranging development finance takes considerably longer than a 28-day auction completion allows, so many buyers use bridging to complete on the land first and refinance into development finance once the build contract is signed.

Red Flags That Should Walk You Away

• Permission that's about to lapse with no realistic route to renewal
• No confirmed access, or access "by way of a track" with no registered right
• A guide price that only makes sense if you ignore finance costs and profit margin
• Conditions requiring a Section 106 payment not disclosed anywhere in the marketing

Bottom Line

Land and plots can be genuinely profitable auction purchases, but only if you price the scheme before you price the land, not after. Run the residual calculation on every lot before you set a bidding limit, treat the guide price as a starting point for research rather than a signal of value, and check today's deals for current land and plot listings alongside finished houses.