[tag:united-kingdom]

Members of Parliament can vote, or not vote, however they like. If they don't tow the party line, then under the [whip](https://en.wikipedia.org/wiki/Whip_(politics)#United_Kingdom) system, they might face the sanction of being suspended or expelled from their party. However, that doesn't make an abstention unlawful, and it doesn't prevent the MP from continuing to sit in Parliament as an independent.