(2 part post):
Skyscanner is a good website but it's not infallible. I certainly hope that it's not offering any Ryanair flights to Helsinki because they don't fly there ;-)
(Ryanair fly from Stansted to Tampere but that means taking the Mobus bus service to Helsinki, which takes 2� hours and adds �25, each way, to your costs).
Blue 1 operate a direct, scheduled service between Stansted and Helsinki Vantaa. They'll fly you out on 26/12 or 27/12 for �70. On 28/12, the price rises to �105. There are no flights on 29/12/, 30/12 or 31/12 (or, if flights exist, they're already fully booked)
The return journey, with Blue 1, is priced at �85 on 01/01. There are no flights on 02/01 (or, more likely, all seats are already sold). On 03/01 the price rises to a whopping �255, before falling back to �85 on 04/01.
The prices quoted for flights with Blue1 don't include taxes and charges. (Add �51 to the total calculated from the prices given).
http://www.blue1.fi/en/
According to the Helsinki Vantaa Airport website, the only other direct flights from the UK are with Finnair (from Heathrow and Manchester) and BA (from Heathrow). You might find flights listed with American Airlines or SAS, but these are only 'code-share' flights which are actually operated by Finnair or BA.