There doesn't appear to be a great deal of academic literature focusing specifically on loop cards, however, Adrian Pinel is well published as you can see by the journal articles and conference papers below that I found by doing an author search with his name.
The British Society for Research into Learning Mathematics has a few published papers authored by Pinel - see links below. He has also written a number of books focusing on learning strategies in mathematics.
I also include a previous E-librarian question about the use of games in teaching primary mathematics.
For access to any journals that your library doesn't subscribe to, I suggest you ask about interlibrary loans as they may be able to order individual articles for you instead.
I hope this helps.
Institute of Education library catalogue
Teaching, learning and primary mathematics. Pinel, Adrian. Publisher: Association of Teachers of Mathematics, Publication date: [2000?]. ISBN: 1898611076.
British Education Index
NOTE: For information about accessing full text articles please read this TTRB article: Access to full text journal articles
Developing collaborative approaches: a secondary mathematics regional partnership, spanning pre-ITE and within-ITE provision. Pages 33-38 in: Proceedings of the British Society for Research into Learning Mathematics day conference held on 20 November 2004 at the University of Sussex, Andrew Noyes (ed.), British Society for Research into Learning Mathematics, 2004. See entry under the editors name for contents of the proceedings, 2004. Pinel-Adrian, Plater-Carol, Dawes-Maria.
90 Minutes on a Sunday Afternoon or: The Proof of the Special MT Issue Is in... Mathematics Teaching, Jun 2002, no. 179, p. 8-10, pp. 3, 0 refs., ISSN: 0025-5785. Pinel-Adrian.
The maths task. A report on the first year of a longitudinal study. Pages 67-72 in: Proceedings of the British Society for Research into Learning Mathematics day conference held on 7 June 2003 at the University of Oxford, Julian Williams (ed.), British Society for Research into Learning Mathematics, 2003. See entry under the editors name for contents of the proceedings, 2003. Pinel-Adrian.
Towards numeracy with progression: benchmarking within a pyramid project. Pages 79-84 in: Proceedings of the British Society for Research into Learning Mathematics new researchers day conference on 17 November 2000 and day conference on 18 November 2000, both held at the University of Surrey Roehampton, Tim Rowland (ed.), London: British Society for Research into Learning Mathematics, 2000. See entry under editor for contents of the proceedings, 2000. Pinel-Adrian, Pinel-Jeni.
Aspects of practising in school mathemathics. In British Society for Research into Learning Mathematics: proceedings of the day conference held at the University of Nottingham, Saturday 1 March 1997 and the University of Oxford, Saturday 7 June 1997. (S.l.): BSRLM, 1997? See entry under British Society for Research into Learning Mathematics for contents of the proceedings, 1997, pp. 87-92. Pinel-Adrian.
What every head should know (about the secondary maths curriculum). Managing Schools Today, October 1996, vol. 6, no. 2, p. 22,24, ISSN: 0968-1558. Pinel-Adrian.
Questions of comparison and beginning. Mathematics Teaching, September 1996, no. 156, p. 14-20, ISSN: 0025-5785. Pinel-Adrian.
Maths knowledge and understanding of primary student teachers: initial findings from a 2 year study. Pages 85-89 in: Proceedings of the British Society for Research into Learning Mathematics day conferences held at University of Warwick, 12th-13th November 1999, Liz Bills (editor), (s.l.): British Society for Research into Learning Mathematics, 1999. See entry under the editors name for contents of the proceedings, 1999. Pinel-Jeni, Pinel-Adrian.
Making sense of maths. Special Children, June 1989, no. 31, p. 10-13, ISSN: 0951-6875. Pinel-Adrian, Boorman-Phil.
‘THE MATHS TASK' - A REPORT ON THE FIRST YEAR OF A LONGITUDINAL STUDY
"In response to a requirement to identify applicants to ITE who are lacking certain defined qualities, a mathematics task was designed. It has now been trialled for 8 months and indications are generally positive. It has three parts - video-, game- and misconceptions-based. The first part - video-based - is outlined here and some of the emerging illustrative data considered. However there are many questions arising from this task that need to be addressed longer term by the project team. As this is intended to become a longitudinal study with several aspects, these questions will be further addressed in later papers by the team."
Follow Me! Mental and Oral Card Games & BEAM Loop Cards
http://www.loopcards.net/ - this is Adrian Pinel's website