Investments in subsidiaries

£000
Cost
Balance at 1 April 2015, 31 March 2016, 1 April 2016 and 31 March 201742,585
Provision
Balance at 1 April 20157,885
Reversal of provision(6,740)
Balance at 31 March 2016 and 31 March 20171,145
Net book value
At 1 April 201534,700
At 31 March 201641,440
At 31 March 201741,440

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 due to local regulatory requirements.

The reversal of the provision in prior year 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.

In FY2017 the Company's investment in it's fully owned subsidiary TR Fastenings Inc was sold at cost to Trifast Overseas Holdings Ltd in a share for share exchange. This led to no change in the net book value of the equity investments held by the company.