If by last year you mean 2015 then the answer is (365* £3.66/2) = £667.95.
The mean average amount saved per day is the mean of 1p (first day) and 365p (last day) which is 183p= £1.83. Multiply this by the number of days in the year (365)
ubasses is of course right if you meant for 2016 by the end of the year