During this period, Dewar was noted for his hostility to "pauper immigration" and played an active part in campaigning for the legislation that became the Aliens Act 1905.

[6] However, as he never married the baronetcy and barony became extinct on his death, at Homestall, in April 1930, aged sixty-six, following which he was cremated at Golders Green Crematorium.

For cycling he donated the Dewar Challenge Shield in 1901, a heavily embossed silver plaque depicting goddesses and allusions to Scotland to include thistles and a profile of a racing cyclist centrally mounted.

It is inscribed "Theatrical Sports Five Miles Cycling Championship Shield" — "Presented by Sir Thomas Dewar MP — To be won Three Years in Succession".

The Dewar Match is a distributed shooting event held in various locations with the results mailed in to determine an aggregate winner.

Dewar's marksmanship trophy is a large silver cup standing over two feet tall with two oversized handles and ornately decorated to the Society of Miniature Rifle Clubs (SMRC) of Great Britain.