The deficit may have gone up because the life expectancy of the members has been raised. Actuarial valuations are notoriously broad brush.
The interesting thing is that the share price has gone up today on the increased profits. That share price takes account of the current deficit in the pension scheme and the dividend policy of BA.
Members of a pension fund have access to the accounts; ask to see them if they haven't already been sent to you. They should show the basis of the valuation.