The form and manner that is established by the UK competent authority is detailed in Article 79 of the ANO 2009 and does not require the recording of flight time under IFR. AMC1 FCL.050 is, therefore, in the case of UK licensed pilots at least, irrelevant in the context of this thread.
The ANO is UK law, which must be complied with. Part-FCL derives from European law, which must be complied with. The CAA have recognised this and, as the Competent Authority, have specified the "form and manner" in CAP804:
Part E Personal Flying Logs and recording of Flight Time
This Part sets out the requirements and guidance for Log annotation. The Part-FCL and Air Navigation Order requirements are listed below so that pilots have the information needed to maintain records that meet both European and national requirements.
1 General information
Flight crew logs must be kept in accordance with the provisions of Article 79 of the UK ANO as amended and must also conform to Part-FCL (AMC FCL.050 refers). Part-FCL states that flight time shall be recorded in a manner specified by the Authority.
2 Required information
2.1 Part-FCL.050 and the ANO require a flight crew member to keep a personal flying log in which at least the following particulars are recorded:
2.1.2 Operational conditions, namely if the operation takes place at night, or is conducted under instrument flight rules.
2.2 Pilots applying for a licence or rating are strongly advised to use a log complying with Part-FCL.050 AMC No.1 to facilitate its issue.
I am not really interested in the legal argument. Section 2.2 says it all: If you want a Part-FCL qualification then comply with the Part-FCL logging requirements.
thing, Don't despair !
You asked a perfectly sensible question on what was required to gain an additional qualification. Then some people assumed you already had it, or should know where to look for the information without asking. A technical discussion ensued and, in the slight drift, some forgot your initial query and missed that it wasn't you who had started it.