Inspiration

New laws change how businesses work, but nobody can easily tell when a law will actually arrive. We wanted to turn that guesswork into a forecast, the way weather forecasts turn uncertainty into “70% chance of rain”.

What it does

Westminster Weather tracks UK government bills from proposal to the moment they take effect, and shows a weather-style status, the chance of becoming law before key dates, and the next milestone. For example: “80% chance of Royal Assent before Christmas.”

How we built it

We collected every UK government bill since 2006 (588 bills) from the Parliament Bills API, tagged their topics with Gemini, and trained an XGBoost model that simulates thousands of possible futures for each bill. We tested it on bills since 2019, using only information available at the time of each forecast.

Challenges we ran into

The data was messy, with misfiled dates and wrongly labelled bills, and our first model was far too pessimistic until we fixed how session endings and the calendar worked. Early forecasts are still hard, because the government decides when debates happen; our average error is around 70 days.

Accomplishments that we’re proud of

Our forecast gets sharper as a bill progresses, from about 100 days off at introduction to about 20 days near the end, and it beats simple rules of thumb at every stage. We built the full pipeline (data, model, API and live demo) in 25 hours.

What we learned

Since 2006, no government bill has lost a vote: bills die when time runs out, at the end of a session or when an election is called. We also learned how easy it is to fool yourself with a model that only looks good on the past.

What’s next for Westminster Weather

We want to add vote and amendment data, use every version of a bill’s text, and send live alerts when a forecast changes. We also want to check that “70%” really means 70%.