The increase would mean the dividend for the year to April would be at least 8.5p a share. Tomkins said that means that if preference shareholders exercise their right to convert, the yield would be equivalent to 6.26 per cent compared to 6.25 per cent on their existing holding.
The preference shares are redeemable in 2013, but holders can opt to convert on 30 September any year until then.
The dividend forecast was accompanied by a statement that trading profit was 'comfortably ahead' of the previous year.
The shares rose 3.5p to 242p.