Highest temperature in London on August 8?

Platform comparison

Market context

The key event is the highest temperature logged at London City Airport on 8 August, with the market resolving off the Daily Observations table rather than the summary box if the two disagree. Polymarket’s live page already had the contract pinned to **28°C** with full crowd confidence, and it notes that revisions within the settlement window can still count until the next day’s first datapoint appears.[1]

That 100% print is easier to read in context: London temperature markets can look binary once the day is effectively locked by observed data, especially when the forecast and the airport feed converge. Comparable London temperature contracts have resolved cleanly on a single Celsius band once the official observation was published, including an August market that settled to **23°C** on Heathrow-based data.[17] The current zero-price alternatives mainly reflect that traders are no longer paying for uncertainty about the upper range, not that the event has changed mechanically.[1]

The main catalysts now are procedural rather than meteorological: whether Weather Underground posts any late revision to the Daily Observations table, and whether a first datapoint for 9 August arrives, which would close the revision window under the market rules.[1] On the crypto side, the contract is a straightforward USDC-settled weather binary, so its mark should mostly track the on-chain order book rather than BTC or ETH direction unless broader risk sentiment spills into prediction-market liquidity. The only material monitoring point is whether any late data correction shifts the recorded peak inside the allowed Celsius band, which would matter more than headline forecasts at this stage.[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

What are crypto prediction markets?

Crypto prediction markets are on-chain smart contracts where you buy YES or NO shares on a future crypto event (e.g. "BTC above $100k by year-end"). The market price between 0¢ and 100¢ is the implied probability.

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.

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%.