Highest temperature in London on August 9?

Platform comparison

Market context

Polymarket is pricing this London temperature contract as a near-certain outcome on **31°C**, with the market implying **0% YES** for the headline “higher” outcome and shares settling against the Celsius band that contains the top reading at London City Airport on 9 August. On Polymarket, traders are effectively positioning USDC on Polygon around a conditional-token payout, so the practical question is not whether London is warm, but whether the Weather Underground **Daily Observations** table for EGLC prints a maximum that lands in the next bracket up or stays in the current one. The market rule matters here: the Daily Observations entry, not the Day High & Low summary, is the source that counts for settlement.[5]

Recent context supports why the crowd has anchored so tightly. Southern and central Britain entered a renewed heatwave spell over the 8–9 August weekend, and by 9 August regional highs across London and the South East were already running around 31°C to 32°C, with the UK having logged 33 separate days above 30°C this year by that point.[1] Earlier in the summer, London had already produced a 26.6°C reading at Kew Gardens that the Met Office described as the hottest day of 2026 so far, which shows the city has been capable of sharp warm-ups even before the late-summer peak.[9]

For traders, the live catalysts are the day’s observation cadence and any late shift in cloud, wind, or sea-breeze timing rather than any scheduled announcement. Forecasts published for 9 August pointed to sunny skies, a high around 32°C, low rain risk, and a light breeze, while similar general August climatology for London still centres well below that level, which helps explain why the order book has concentrated around a single band rather than spreading across multiple outcomes.[4][11] Because settlement is tied to the first datapoint for the following date only after the relevant window closes, late revisions to the Wunderground table can still matter until that cutoff.[5]

Sources: 1 · 2 · 3 · 4 · 5

Methodology

This page reviews Highest temperature in London on August 9? across five venues. The live probability is the Polymarket mid-price, sourced directly from the on-chain Polygon order book; the comparison columns benchmark each venue on fee structure, KYC, settlement currency and payment rails. Every CTA routes to Kalshi UK, which mirrors the Polymarket order book at 0% fees.

Resolution & payout

At resolution the UMA oracle takes over: a proposer posts the outcome with a bond, any token holder can dispute within two hours. Without dispute the result is accepted and the smart contract distributes USDC instantly.

On Kalshi (CFTC-regulated) resolution runs through their in-house clearing engine in USD. Betfair Exchange settles after match end in the account's local currency. Manifold pays no cash — only its in-platform "mana" currency.

UK Frequently Asked Questions

What's the difference between YES and NO shares?

A YES share pays $1.00 if the event happens, $0 otherwise. A NO share pays $1.00 if the event doesn't happen. The market price between 0¢ and 100¢ is the implied probability.

What does Polymarket cost to trade?

Polymarket itself charges 0% — the only cost is the Polygon network fee, typically under $0.01 per transaction. Off-chain venues like Kalshi or Betfair charge 2-7% commission.

Is Polymarket legal in the UK?

Polymarket is accessible to UK traders but is not UKGC-licensed. It operates under US CFTC jurisdiction. UK residents face no domestic legal prohibition on using it, but UKGC consumer protections do not apply. For UKGC-regulated alternatives, Betfair Exchange and Smarkets offer similar prediction-style markets.

Do I pay tax on prediction market profits in the UK?

UKGC-licensed platform profits (Betfair, Smarkets) are typically tax-free gambling winnings for UK individuals. Polymarket profits involve USDC crypto transactions, which HMRC treats as Capital Gains Tax events. Keep full transaction records and report via Self Assessment if gains exceed £3,000 per tax year.

How do I deposit on Polymarket from the UK?

UK traders typically fund Polymarket via Coinbase UK, Kraken or Revolut — buying USDC with GBP and transferring to a Polygon-compatible wallet (MetaMask, Coinbase Wallet). Polymarket's onboarding walks you through the bridging process. Typical GBP-to-USDC conversion costs 0.5–1%.