options are fundamentally priced based on the expected move of the underlying. The price of the straddle indicates the 1 standard deviation expected move (i.e. 68% probability of the price staying in that range).
When markets gapped open this morning, the perceived expected move of Britannia increased (iv increase). This makes the ce options go up even though the underlying fell.
Edit: Also, the futures&options market are one. So, if futures go up, so will the synthetic future of options. In case of Britannia, the underlying fell but the futures went up & so did the ce option prices.