Richard is right to mention price and I have always found Bloomsbury excellent value for money. Also under £100 each the Wildy Practitioner Guides on Probate, Wills, Probate Disputes and 1975 Act claims, the first 2 with an accompanying CD. They are all about 3 years old now and no word yet on updates.
Sole practitioners and small firms must wince at £500 a go. After retirement I have become more frugal. Student books (no precedents) tend to be amazing value. The latest Moffat on Trusts 7th ed is 1080 pages for £37. Scrooge here updated his 5th edition to 6th recently by a second hand purchase for £2!
I doubt I will ever update my Underhill or Lewin. I am however going to splash out in December on the next Chamberlain/ Whitehouse Trust Taxation etc at (semble) £235 or ask Santa to oblige (despite my shortcomings over the past year). Tremendous scholarship.