The HMRC Personal Wealth Statistics for 2008-10 estimates the number of UK individuals aged 65 or over in the identified wealth population (i.e. wealth owned by estates represented by those passing through probate) with assets over £1 million to be 106,000, of which 30,000 have assets over £2 million.
This is published in the HMRC National Statistics table 13.3 available at https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/270429/table_13-3.pdf
A breakdown of these figures at a sub-UK level is not available.
Alternative estimates based on the Office for National Statistics' Wealth and Assets Survey are not directly comparable with the HMRC Personal Wealth Statistics, as they are (i) based on households rather than individuals, (ii) use a different definition of wealth which, for example, includes the value of private pension funds.
Table 2.14 of Wealth in Great Britain Wave 3 (2010-12) shows that 11% of UK individuals aged 65 or over live in households where household total wealth is at least £1 million. This Table is available here:
Figures for the proportion of individuals in households with total wealth of at least £2 million are not published by the Office for National Statistics, nor are these figures at a sub-UK level. Further information on Wealth in Great Britain can be found here: http://www.ons.gov.uk/ons/rel/was/wealth-in-great-britain-wave-3/2010-2012/index.html
 In the Wealth and Assets Survey, total wealth of a household is a net wealth measure for each household created by adding together the different types of household wealth; property wealth (net), financial wealth (net), physical wealth and private pension wealth. It should be noted that it does not include business assets, accrued rights to state pensions or assets held in Trusts.