Those who want the UK to stay in the single market and customs union tried to amend the Queen’s speech in 2017 to require this. They lost by 322 to 101 votes.
They tried again with an amendment to the EU Withdrawal Bill in the Commons. They lost again by 322 to 99, by a slightly wider margin.
On each occasion the official Labour position was to abstain, as they seem to be very divided over this matter and unable to make up their minds on a single united view.
Both the official Leave and remain campaigns made it quite clear leaving the EU meant leaving the single market and customs union. The government also pointed this out before the vote, and the EU has consistently stated you cannot be in the single market and customs union whilst refusing freedom of movement and ceasing to make budget contributions.