Group£m
At 1 April 20123.3
Additions3.0
Disposals(0.9)
Currency translation differences0.3
At 31 March 20135.7
Additions1.9
Disposals(0.1)
Currency translation differences(0.6)
At 31 March 20146.9

During the year, the group increased its investment in Muharraq Holding Company 1 Limited by £1.9 million and disposed of its loan stock investment in WRc Plc for consideration of £0.1 million.

At 31 March 2014, the group's investments mainly comprised its investment in Muharraq Holding Company 1 Limited. These investments are held at fair value.

Details of principal operating subsidiary undertakings and joint ventures are set out below. These undertakings are included within the consolidated financial statements. A full list of the group's subsidiary undertakings is included in the company's annual return.

Class of share
capital held
Proportion of
share capital
owned/voting
rights %*
Nature of business
Subsidiary undertaking
Great Britain
United Utilities Water PLCOrdinary100.0Water and wastewater services and network management
United Utilities Property Services LimitedOrdinary100.0Property management
Joint ventures
Estonia
AS Tallinna VesiOrdinary35.3Contract operations and maintenance services

* Shares are held by subsidiary undertakings rather than directly by United Utilities Group PLC.

Joint management of AS Tallinna Vesi (Tallinn Water) is based on a shareholders' agreement. Tallinn Water's financial year end is not coterminous with that of the group. The most recent financial year ended on 31 December 2013.

In relation to the group's interests in joint ventures, the assets, liabilities, gross income and expenses are summarised below:

Group share of joint ventures2014
£m
2013
£m
Non-current assets44.846.8
Current assets19.317.5
Non-current liabilities(28.3)(28.2)
Current liabilities(7.5)(8.0)
28.328.1
Group share of joint ventures2014
£m
2013
£m
Gross income15.615.1
Expenses(8.3)(7.4)
Taxation(1.4)(1.3)
Profit after taxation5.96.4

The joint ventures have no significant contingent liabilities to which the group is exposed. The group has issued guarantees of £5.2 million in support of its joint ventures (2013: £5.2 million) which are included in the contingent liabilities total disclosed in note 27.

CompanyShares in
subsidiary
undertakings
£m
Cost
At 1 April 2012, 31 March 2013 and 31 March 20146,326.8
Impairment
At 1 April 2012, 31 March 2013 and 31 March 2014(726.8)
Net book value at 31 March 2013 and 31 March 20145,600.0

During the year ended 31 March 2014, a review has been performed supporting the carrying value of the £5,600.0 million investment in United Utilities PLC. As in the prior year, the review considered a 'fair value less costs to sell' valuation and whether there were any indications that the value of the underlying business may have changed. No indications of impairment or impairment reversal were identified.