Absolutely not. You must discuss your proposal with the Building Inspector, who almost certainly will tell you that you must continue to put the stormwater into a soakaway. If you disagree or fail to act upon what the Building Inspector tells you then your Council will serve you with a legal notice. Failure to comply with such a notice means that the Council will arrange for the work to be done 'in-default', and its costs (which can be very expensive) recharged to you.