Can you post a link next time?
I priced it out:
https://www.google.ca/flights/#searc...LSIN0AY81;sc=b
The problem is the A350 from LHR-HEL only runs in the morning, so you will have to overnight at LHR.
If you stopover in LHR, it will also be very expensive and you also get hit with the luxury tax.
Also mention that it's in CAD, as this works out to be around $1.5k USD
It should also be moved to Premium Fare Deals