Highest temperature in London on August 9?

Platform comparison

Market context

London’s outcome will be set by the highest Celsius reading logged at London City Airport on 9 August, as recorded in Weather Underground’s Daily Observations table rather than the summary high/low panel. That makes the market a clean read on one station’s intraday peak, with settlement depending on the exact published observation history rather than broad London averages or forecast highs.[4]

The current 0% YES implies the crowd sees the stated temperature band as effectively locked in, even though nearby sources point to a hot spell rather than an extreme outlier. Regional reporting for 9 August placed London and the South East around 31–32°C, while a separate daily weather page showed London’s latest observation near 63°F overnight UTC, consistent with a much cooler starting point before the daytime maximum is reached.[1][2] In earlier London heat episodes, forecast highs of 31–32°C have often translated into a final airport-station peak within that range, so the key question is whether the official observation at EGLC lands just above or below a band boundary.[3][5]

For a market settled in USDC, the main catalysts are the final station observations and any late-day revisions before Weather Underground closes the date’s record. Because the market resolves off the published daily table, a trader should watch whether the station posts a late-afternoon or early-evening value that edges into a higher bracket, since the 12:00 UTC settlement window means the live on-chain price can stay fixed while the underlying weather print still evolves. Broader crypto conditions matter only indirectly here, but a sharp BTC or ETH move, or heavy USDC flows, can still distort liquidity and make the displayed probability less sensitive to the last meteorological update.

Sources: 1 · 2 · 3 · 4 · 5

Methodology

Methodologically this overview focuses on on-chain pricing: Polymarket's live mid comes from the Polygon conditional-token order book and settles automatically in USDC. The other three venues — Kalshi, Betfair, Manifold — sit alongside as off-chain reference points so you can see how the contract translates across regulatory and settlement regimes.

Resolution & payout

Settlement is on-chain via UMA Optimistic Oracle. A proposer posts the outcome with a bond, a two-hour dispute window opens, then the smart contract lifts winning conditional tokens to 1 USDC and sends payments to holders' wallets automatically. No withdrawal fees beyond Polygon gas.

Off-chain venues (Kalshi, Betfair, Smarkets) settle in local fiat through bank-side clearing — faster than SWIFT, slower than on-chain. Manifold pays no real cash.

UK Frequently Asked Questions

Why USDC and not ETH or USDT?

USDC is the Polygon standard — audited reserves (Circle, monthly attestation), deepest order book, low gas costs. ETH volatility would distort probability quotes; USDT has thinner Polygon liquidity than USDC.

What does a transaction cost on Polygon?

Polygon gas is typically under $0.01 per transaction. A full trade cycle (Approve + Order + Fill) totals around $0.03 — compared to $5-50 on Ethereum mainnet.

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%.