FWIW, spending isn't always massively different. In 2015 it was £15.6m for the Tories vs £12.1m for Labour (https://www.prweek.com/article/1380236/uk-general-election-s...) - not a huge difference.
I've had 6 weeks of adverts aimed at a target tory/labour seat I live very close to in the North West, all from 3rd parties. The first 5 weeks it was mainly unknown groups like "Working for UK" and "Campaign Against Corbyn", all personal attack adverts on Corbyn (leader of the labour party), and when I dig deep I find the people behind these new companies (often set up in the last month or two) are people like a Conservative Councillor in London, or an Ex Conservative MP from Surrey.
In the last week there have been some "tactical voting" adverts from more establish groups (peoples vote etc)
I guess this is a way for the conservatives to get around spending limits, I guess like U.S. "Super Pacs"
The Super Pacs is a good example - it does sound like the Tories are (worryingly) going down this route.
Labour (incumbent) have mostly been quiet in this HEAVILY remain-voting area, with a leaflet or two highlighting a "People's Vote". The LibDems have parachuted in a Tory defector, and have been absolutely going all out with the campaigning around "Revoke Brexit".
The Conservatives have been quietly content to stay out of the way and watch the non-Leave vote split between the former two.
Labour had no chance this year due to a shift in demographics, not to mention the fall in Labour vote share