I don't see how LIBOR could be fixed by one or even two or three banks acting alone or in cahoots

Thomson Reuters is the designated calculation agent for BBA LIBOR. Data submitted by panel banks into the bbalibor process is received and processed by Thomson Reuters and the data is calculated using guidelines provided by the FX&MM Committee.
Each cash desk in a LIBOR contributor bank has a Thomson Reuters application installed allowing that institution to confidentially submit rates. Each morning between 1100 and 1110 a named individual responsible for cash management at each panel bank formulates their own rates for the day and inputs them into this application, which links directly to a rate setting team at Thomson Reuters.  A bank cannot see other contributor rates during the submission window - this is only possible after final publication of the BBA LIBOR data. Thomson Reuters run a collection of automated and manual tests on the submitted rates before they are sent to the calculation engine, and after calculation the data is released to the market via Thomson Reuters and other licensed data vendors.
Every bbalibor rate produced by Thomson Reuters is calculated using a trimmed arithmetic mean. Once Thomson Reuters receive each contribution submission they rank them in descending order and then exclude the highest and lowest 25% of submissions - this is the trimming process. Details of this are shown in the table below. The remaining contributions are then arithmetically averaged to create a bbalibor quote. This is repeated for every currency and maturity, producing 150 rates every business day.

No. of Contributors	Trimming methodology	No. of Contributors on which BBA LIBOR rate is based
18 Contributors	top 4 highest rates, tail 4 lowest rates	10
17 Contributors	top 4 highest rates, tail 4 lowest rates	9
16 Contributors	top 4 highest rates, tail 4 lowest rates	8
15 Contributors	top 4 highest rates, tail 4 lowest rates	7
14 Contributors	top 3 highest rates, tail 3 lowest rates	8
13 Contributors	top 3 highest rates, tail 3 lowest rates	7
12 Contributors	top 3 highest rates, tail 3 lowest rates	6
11 Contributors	top 3 highest rates, tail 3 lowest rates	5
10 Contributors	top 2 highest rates, tail 2 lowest rates	6
9 Contributors	top 2 highest rates, tail 2 lowest rates	5
8 Contributors	top 2 highest rates, tail 2 lowest rates	4
7 Contributors	top highest rate, tail lowest rate	5

The decision to trim the bottom and top quartiles in the calculation was taken to exclude outliers from the final calculation. By doing this, it is out of the control of any individual panel contributor to influence the calculation and affect the bbalibor quote.

That's all from the British Bankers Association explanation of how the LIBOR rate is calculated. Note that outliers are excluded as they use a trimmed arithmetic mean which excludes the highest and lowest 25% of submissions.

This being the case, the current attacks on Barclays seem a touch excessive. For LIBOR to be reduced there must have been other banks involved, who were they. Also for other banks to be involved I sense a direction or at least a 'steer' from the Bank of England or the Treasury that this is what was wanted/needed.