One of the more notable reasons to use 1918 as cut-off is that it represented a high water mark in the number of MPs in Westminster. The Parliament Act of 1911 also functionally altered the balance of power between the Commons and the House of Lords, which has made Commons defeats much more significant. Indeed more peers than commoners served as premier in the 19th century.
Making comparisons with other votes throws up some difficulties. Your title question is currently "Has there ever been a larger UK Parliamentary defeat than on Brexit tonight?". The majority was 230 votes. For comparison :
In the current administration SNP opposition day motion (with no legal force) on the 29th November 2017 passed 288 to 0, with all government MPs abstaining.
Something very similar apparently occurred on 11th March 1977, with an opposition motion to adjourn passing 293-0 [I haven't been able to find this in Hansard yet].
If you wish to limit yourself to defeats on government motions, the People's Budget was defeated on November 30th by 350 votes to 75 in the House of Lords in 1909. This parliamentary defeat (though not a Commons one) was the action which precipitated the Parliament act.
If you want to further limit yourself to Commons defeats, I'm not aware of any, however Hansard, the transcript of record on parliamentary business only lists the results all divisions since 1909, with a somewhat spottier record back to the point the British parliament became the UK one following union with Ireland. If you want to search yourself, I suggest you start here.