It will look at the costs and benefits, with a “go or no-go" decision by the end of the year.
Rescuers searching for six-year-old Lucas Dobson, who fell into a river on Saturday, have found a body.
It comes after the PM said the plan to avoid a hard border in Northern Ireland was "anti-democratic".
People across the UK flood police with gifts and kind acts in the wake of PC Andrew Harper's death.
Office blocks are also being used to house families as 210,000 children are estimated to be homeless.