Preheat the oven to gas mark 4/180°C/fan 160°C. Grease and line a 20cm square baking tin.
In a large, heavy bottomed saucepan, melt together the butter, sugar and syrup until smooth. Stir in the oats and coconut then scrape into your prepared tin, smooth flat and bake for 20 - 25 minutes, until golden and firm. Remove from the oven and allow to cool in the tin.
To make the topping, melt the white chocolate then stir in the oil. Melt the dark chocolate in a separate bowl. Pour the white chocolate over the flapjacks (still in their tin) then drizzle over the melted dark chocolate, using a fork to create swirls.
Space out the Guylian chocolate Sea Shells on top of the chocolate, so that you get one sea shell in the centre of each flapjack. Refrigerate until the chocolate has set then slice into squares.