Highest temperature in London on August 9?

Platform comparison

Market context

Polymarket is pricing this London temperature contract at **0% YES**, so the crowd is effectively treating the listed outcome bands as dead money for today’s move rather than assigning any meaningful chance to a specific Celsius range. Settlement is tied to the **Daily Observations** table for London City Airport Station on Weather Underground, and the market pays out through the usual Polymarket mechanics: USDC collateral, Polygon-based conditional tokens, and redemption only for the winning temperature band once the data source is finalised.

That near-zero price looks extreme against London’s August climatology, where typical highs sit in the low 20s Celsius, but it is still consistent with a market that is focused on the exact resolution band rather than the headline forecast. The broader historical frame is that London can spike sharply during late-summer heat events: in the 2022 UK heatwave, London-area stations pushed into the mid-30s Celsius, while the city’s all-time August extremes are far above normal summer levels. Polymarket’s own market page has shown the contract leading at **31°C** with **32°C** as the main alternative, reflecting a live market that is concentrating on a fairly tight heat-range outcome rather than a broad binary view.[1][10][17]

For traders, the main catalyst is the actual station readout on Weather Underground, not the city forecast headline, because the market resolves off the highest logged Daily Observations value for the day and can still incorporate later revisions until the next date’s first datapoint appears.[1] On a practical Polymarket basis, that means the key watchpoints are the timing of afternoon warmth, any late-evening updates, and whether London City Airport records a brief peak above the expected band; recent weather commentary has pointed to warm, sunny conditions in London around this period, which is exactly the sort of setup that can move a thin market even when the crowd has already priced in a dominant outcome.[1][5][7]

Sources: 1 · 2 · 3 · 4 · 5

Methodology

Methodologically we separate two layers: the live probability (Polymarket mid-price) and the platform attributes (fee, KYC, settlement currency, payment rails). That keeps the comparison honest — a single canonical probability across the row, with the venue-by-venue trade-offs spelt out in the columns next to it.

Resolution & payout

Polymarket-based markets settle through the UMA Optimistic Oracle on Polygon. A proposer submits the outcome, a two-hour challenge window opens, and unchallenged proposals finalise the resolution. Payouts settle automatically in USDC the moment the result is final — no bookmaker, no delay.

Kalshi-based markets settle in USD via the CFTC-regulated clearinghouse. Betfair Exchange settles in GBP/EUR net of commission. Manifold is play-money and does not pay out real funds.

UK Frequently Asked Questions

Is this market available outside the US?

Polymarket itself is geo-blocked in the US/UK/EU. Always check the legal status of prediction markets in your jurisdiction before trading.

How does resolution work?

Through the UMA Optimistic Oracle on Polygon: a proposer submits the outcome, a two-hour challenge window opens, and USDC payouts settle automatically once the result is final.

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%.