During the debate on the Sale of Students Loans Bill there was an exchange between Lib Dem MP,  Stephen Williams  and the  Tory front bench spokesperson on Higher Educaton and Reading East MP, Robert Wilson, which went thus:

Stephen Williams: Like me, the hon. Member for Reading, East got interested in politics in the 1980s—I believe that we were in the same party at that point.
Mr. Wilson: No, we were not.
Stephen Williams: We have been in the same party at one point.
Mr. Wilson: No, we have not.
Stephen Williams: We were both members of the Social Democratic party once.
Mr. Wilson: No, I was not.
Stephen Williams: I stand corrected.
Mr. Wilson: I was not!
Madam Deputy Speaker (Sylvia Heal): Order. May we please have order in the debate?
Stephen Williams: I find it ironic that Conservative Front Benchers have tabled the amendments, whatever political perspective the hon. Gentleman supported in the 1980s. In all its privatisations in the 1980s and 1990s, the Conservative party did not necessarily guarantee full value for money for the taxpayer— [ Interruption. ] The hon. Gentleman looks sceptical—let me give the example of the Royal Ordnance sell-off or even the railway sell-off.

(Hansard 23 january 2008 Column 1542 - 3)

The reason this might be of any interest is that it is aleged (see here and here) that Robert Wilson MP stood in Redlands Ward for the SDP in 1988 and 1989 with a result in 1988 of:

Dimmick (Lab) 1460
Oliver (Con) 1005
Wilson (SDP) 393
Lazenby (SLD) 367

So.  Was Robert Wilson, former President of Reading University Students Union, a member of the SDP when he stood for them in Redlands Ward in the heart of the Reading East constituency he now represents, or was he not a member?  By that thread hangs a defence against any potential charge of lying to the House of Commons.  See also here.