Highest temperature in London on August 8?

Platform comparison

Market context

Polymarket is pricing this London Airport temperature contract at **100% for 28°C**, so the market is effectively treating that outcome as locked in rather than merely likely. On Polymarket, traders hold and swap **conditional tokens** for USDC on **Polygon**, and a winning share settles at $1 if the resolved band matches the highest recorded temperature in Weather Underground’s Daily Observations table for London City Airport Station on 8 August 2026.[1]

For context, that 100% reading should be read against London’s late-summer distribution rather than against a single forecast. AccuWeather’s London monthly view showed **81°F/60°F** for 8 August, which is broadly consistent with a high around 27–28°C, while long-run August averages for London are closer to the low 20s Celsius.[2][7] The same event page also notes trading volume of **$77.8K**, which matters because a market with that level of participation can still be sticky even when the price already sits at the ceiling.[1]

The main catalysts a trader would watch are the airport observations themselves and any revisions before Weather Underground publishes the next day’s first datapoint, because Polymarket says late changes within the resolution window can still count until that cutoff.[1] On the public-health side, the UK Health Security Agency had a **Yellow Heat-health alert** in force for London from 8 August 09:00 until 11 August 21:00, reinforcing the warm conditions that likely anchored the 28°C consensus.[9] The practical issue for settlement is not the day’s general weather headline but whether the specific station observation in Wunderground’s Daily Observations lands inside the listed range.[1]

Sources: 1 · 2 · 3 · 4 · 5

Methodology

We track Highest temperature in London on August 8? across the five venues with material prediction-market liquidity. The probability shown is the live Polymarket mid; the comparison rows summarise how each venue treats the underlying contract — fees, KYC thresholds, settlement currency, deposit options. The highlighted row marks the cheapest route into Polymarket's order book.

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

Where can I trade this market with the lowest fees?

Polymarket is geo-blocked in the US/UK/EU. The easiest 0%-fee broker into the same order book is PolyGram. Kalshi charges up to 7% per trade; Betfair Exchange takes 2-5% commission on net winnings.

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.

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%.