In a direct communication, the source explained:

In compliance with the Statistical Code of Practice under section 5.3.1 we have decided to suppress the series IUMBV24 [bank tracker mortgages] due to confidentiality reasons. The series may, in the future, be unsuppressed when we feel the rate is representative of market conditions.

Unfortunately, for the series IUMAAJLT and IUMAJLT [sovereign yields], no data is available because the Bank has been unable to source sufficient representative data to allow it to calculate an average rate.

In response, we have archived the series by marking them as "discontinued" in their metadata and catalog location. Figures are percent per annum (%). Date ranges vary.

The series reside in the historical catalog (United Kingdom » Banking » Average quoted household interest rates » Secured lending (mortgage) rates) and is:

• BOEIUMBV24M.IGBR  = [DISCONTINUED] Bank & Building Societies: Weighted average interest rate - End of month - Bank rate tracker mortgage (75% LTV), (%) - January 1997 to August 2017

And in (United Kingdom » Financial » Interest Rates » Sovereign debt (gilts)):

• BOEIUMAAJLTM.IGBR = [DISCONTINUED] Monthly average of yield from 2.5% Index Linked Treasury Stock 2016, (%) - February 1983 to July 2016
• BOEIUMAJLTM.IGBR  = [DISCONTINUED] End month level of yield from 2.5% Index Linked Treasury Stock 2016, (%) - January 1983 to June 2016

And in (United Kingdom » Financial » Interest Rates » Wholesale interest and discount rates):

• BOEIUMAJNBM.IGBR  = [DISCONTINUED] Discount rate: End of month level - 3 month Treasury bills - Sterling, (%) - January 1975 to June 2017
• BOEIUMAAJNBM.IGBR = [DISCONTINUED] Monthly average rate of discount: 3 month Treasury bills - Sterling, (%) - Same

Because catalog locations are subject to change, the upper-right search box on DataBuffet.com provides a "find in catalog" mode that accepts a mnemonic.