Highest temperature in London on August 10?

Platform comparison

Market context

London’s temperature on 10 August will be decided by the highest reading logged at London City Airport on Weather Underground, with the market settling into one Celsius band rather than an exact figure. The current crowd price of 0% YES means the contract is not yet implying any meaningful probability for the relevant band, so traders are effectively waiting for the day’s realised peak to come into view. The source rules also matter: the Daily Observations table is primary, and late revisions can still count until the first datapoint for the following day appears.[1]

For context, early-August London temperatures often sit in the mid-20s Celsius, but the city can still spike sharply during settled summer patterns. London’s August average high is around 26°C, while the wider UK has seen much hotter 10 August readings in past years, including the 38.5°C national August record in 2003 and 36.4°C at Heathrow during a later August hot spell.[3][5][7][8] That history suggests the market is usually about whether London lands in a modestly warm band such as 24–27°C or breaks higher on a brief convective surge, rather than about extreme national records.[9][11]

The main catalysts are the near-term weather model updates, any fresh Met Office or UK broadcaster forecast shifts, and the airport’s own observation timing as the settlement window runs to 12:00 UTC. Because the contract is on-chain and USDC-settled, the price can react quickly if late-morning revisions point to a different daily maximum, especially when the first part of the day already locks in a strong high. Broader crypto conditions are secondary here, but BTC and ETH volatility can still affect order-book depth and funding-driven risk appetite across prediction markets if traders are rotating capital between venues.[1]

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%.