Investments in subsidiaries

£000
Cost
Balance at 1 April 201441,436
Additions27,231
Disposals(26,082)
Balance at 31 March 2015, 1 April 2015 and 31 March 201642,585
Provision
Balance at 1 April 2014 and 31 March 20157,885
Reversal of provision(6,740)
Balance at 31 March 20161,145
Net book value
At 1 April 201433,551
At 31 March 201534,700
At 31 March 201641,440

Details of principal subsidiary and associate undertakings, country of registration and principal activity are included in note 33.

All subsidiaries have a reporting date concurrent with Trifast plc, except TR Formac (Shanghai) Pte Ltd which has a reporting date of 31 December.

The reversal of the provision relates to TR Fastenings Inc. An impairment review was conducted using the value-in-use methodology and this determined that the asset is now fully recoverable. The main event leading to the reversal is the turnaround in the business from loss making to a position of sustained profitability. The improved performance for TR Fastenings Inc is forecast to continue in the future and therefore the Board are confident the value is recoverable. The key assumptions used in the impairment analysis are: a terminal growth rate of 2.0%; a post-tax discount rate of 7.8% and a pre-tax discount rate of 13.5%. There has been no impact in the Consolidated financial statements as only goodwill was impaired at this level and IAS 36 prohibits the reversal of impairment for goodwill.