Costain Regulatory News (COST)

Costain Group PLC

("Costain" or "the Company")

Deferred Share Bonus Plan

This notification is made in accordance with DTR 3.1.4(1)(a).

On 19 April 2010, awards over ordinary shares in the Company were made to certain directors of the Costain Group PLC (the "Company") under the Costain Deferred Share Bonus Plan (the "Plan").

The awards granted under the Plan are structured as follows:

1) an option with a nil exercise price over a number of shares ("Deferred Award"); and

2) an option with a nil exercise price over a fixed value of shares, which is granted in combination with an HMRC approved market value option ("Combined Deferred Award").

Under the Schedule to the Plan, the relevant directors were also granted an HMRC approved option over a fixed number of shares with an exercise price of 24.25 pence per share ("Option").

No consideration was paid for the grant of the Deferred Award, Combined Deferred Award and Option (together, the "Awards").

The value of the shares under the Combined Deferred Award and the Option are equal. The Combined Deferred Award and the Option must normally be exercised at the same time. When calculating the maximum value of the shares under a Deferred Award that may be granted under the terms of the Plan, the value of the shares under the Option is not counted.

The Awards will become exercisable on the second anniversary of the date of grant subject to the continued employment of the participant. The value of the shares delivered under the Combined Deferred Award on exercise is the same as the value of the shares under that award at the time of grant. The number of shares under the Deferred Award and Option at grant will be delivered to the participants on exercise.

To the extent that all or any part of an Award becomes exercisable, it remains exercisable until the tenth anniversary of the date of grant.

The Company was informed of the above transactions under the Plan on 19 April 2010.

20 April 2010