The given statement that "lithium is the strongest reducing agent" in Group IA (the alkali metals) as ionisation potential decreases down the group is actually false. The reasoning behind this conclusion involves understanding the concept of reducing power among alkali metals.

Reducing agents are substances that can donate electrons to other substances and thereby reduce them. The reducing strength of an element, especially metals, can often be attributed to its ability to lose electrons easily.

Ionisation potential is the energy required to remove the most loosely held electron from an atom to form a cation. In the case of alkali metals, the ionisation potential indeed decreases as we move down the group; for example, from lithium (Li) to cesium (Cs). This decrease is due to the increasing size of the alkali metals, where the outermost electron becomes increasingly distant from the nucleus and is subjected to a lesser effective nuclear charge. Thus, it is easier to remove the outermost electron in cesium compared to lithium.

Despite lithium having the highest ionisation potential in its group, suggesting it holds onto its electrons more strongly than its counterparts, lithium is not the strongest reducing agent in the group. The decreasing ionisation potential correlates with an increase in the reducing power down the group. Thus, elements like cesium or francium (at the bottom of the group) are stronger reducing agents because their lower ionisation energy makes them more prone to lose electrons and reduce other elements.

Therefore, among the alkali metals, cesium or francium, and not lithium, would be considered the strongest reducing agents. The initial assumption in the statement that a higher ionisation potential (resulting in the harder release of electrons) makes lithium a stronger reducing agent is incorrect. The lower the ionisation potential, the easier it is for the atom to lose an electron and act as a reducing agent.