Flights to Cape Town in Nov/Dec - is this scenerio possible?

I need to fly to Cape Town in November and December however the flights are looking to be quite pricey. Is it possible to do the following for example:
Fly London - Cape Town on the 15th November returning to London on the 31st December.
Fly Cape Town - London on the 25th November returning to Cape Town on the 20th December.
This works out to be about £700 cheaper! Or do you think this will get flagged down?
I will be checking in Luggage both ways.
The flights have increased dramatically over the xmas period compared to to previous years!
Fly London - Cape Town on the 15th November returning to London on the 31st December.
Fly Cape Town - London on the 25th November returning to Cape Town on the 20th December.
This works out to be about £700 cheaper! Or do you think this will get flagged down?
I will be checking in Luggage both ways.
The flights have increased dramatically over the xmas period compared to to previous years!