https://civillitigationbrief.wordpress.com/2016/04/27/what-is-meant-by-a-significant-development-amending-the-costs-budget-when-claim-doubles-in-size-claimant-gets-the-boot/
Where the developments in a PI claim were "capable of being envisaged at the time of the original costs budget" the Master's decision to refuse an increase in the budget was upheld.