Complex sentence: Douglas was successful in overturning a 9065 majority for Angus winning with 22,637 votes, 47.6% of the votes cast, a 16.5% swing to the Conservatives Having won a seat at Westminster, Douglas resigned from his Holyrood seat in the Scottish Parliament.
Split into simpler sentences: Douglas was successful in overturning Robertson's 9,065 majority with 22,637 votes, 47.6% of the votes cast, gaining a 16.5% swing to the Conservatives. Having gained a seat at Westminster, Douglas resigned from his Holyrood seat in the Scottish Parliament.