There is alot of information on the Vodafone/Verizon demerger on the Vodafone website but all the information you really need to apportion the cost of the original Vodafone shares between the new holding of Vodafone shares, the holding of Verizon shares and the cash received as capital is here
The original Vodafone holding cost £8,706. The new Vodafone holding was worth £6,666 and the new Verizon holding was worth £3,732 after the demerger. The combined value of the new holdings was £10,398. The cash received from Vodafone was £1,490. The total value was, therefore, £11,888. The cost is apportioned as follows:CASH £1,490
(£1490 / £11,888) X £8,706 = £1,091. The gain on the cash is £399 (£1,490 - £1,091), £199.50 each.2750 VODAFONE SHARES
(£6,666 / £10,398) x £7,615 (£8,706 - £1,091) = £4,882132 VERIZON SHARES
(£3,732 / £10,398) x £7,615 (£8,706 - £1,091) = £2,733. The fractional cash received of £17 is deducted from £2,733 to leave a base cost of £2,716. As the shares were sold for £3,662, you made a gain of £946, £473 each.
I hope this helps but let me know if you have any further questions.