Calling the referendum and declaring article 50 were passed by majority votes in the House of Commons.

Which party had the overall majority in the house of commons when those items were passed, Stanron? I think it could be you not getting that a party with an overall majority in the commons is quite capable of passing legislation with no help from the rest of parliament. The opposition when these things were passed could moan and whinge as much as they wanted but they had no teeth and could not have stopped them if they tried.

Labour leader Jeremy Corbyn had imposed a three-line whip - the strongest sanction at his disposal - on his MPs to back the bill (to issue article 50).
BBC Here
Even though the Tories had a majority in the House, Labour (in general) did not oppose the issuing of article 50.