The following information relates to three companies that use the revaluation model in relation to intangible assets and prepare annual financial statements to 31 December:
(a) Company W acquired an intangible asset for £250,000 on 31 December 2016. This asset was revalued at £225,000 on 31 December 2017 and at £270,000 on 31 December 2018.
(b) Company X disposed of an intangible asset on 31 December 2018. This asset had been acquired some years previously at a cost of £100,000 and had a carrying amount of £160,000 on the date of disposal. Disposal proceeds were £195,000.
(c) Company Y acquired an intangible asset for £80,000 on 31 December 2016. This asset was revalued at £90,000 on 31 December 2017 and at £65,000 on 31 December 2018. 

Describe the circumstances in which the revaluation model may be used (in accordance with the requirements of IAS38) and explain how each of the above matters should be dealt with in the financial statements of the company concerned.