There does seem to be some evidence to support this assertion, but the resurgence in the popularity of spiritualism ("a belief that spirits of the dead communicate with the living usually through a medium") actually happened during the First World War and continued well into the 1930s. David Nash, professor at Oxford Brookes University, writes that:
Britons had been drawn to ‘irrational’ ideas and practices in growing
numbers long before the Armistice of 11 November 1918. Interest in
spiritualism surged dramatically in 1917, as the nation endured a
third full year of conflict. In fact, at one point, this religious
movement – which promised believers the prospect of being able to
communicate with the dead – briefly threatened to become more popular
than the Anglican church.
Source: David Nash, 'The rise of spiritualism after WW1' (2020)
Spiritualism, which had come to Britain from the US in the mid 19th century, had seen its popularity decline by the early 20th century, but the First World War reversed that trend. Kyle Falcon, who completed a PhD thesis 'Ghosts of the First World War: Spiritualism and Psychical Research in Britain', notes that:
Jay Winter and other scholars have argued that Spiritualism was
appealing to Britons during the Great War because it offered bereaving
family members the pragmatic comfort and communication that
traditional religions and prayer could not provide.
The aforementioned Jay Winter notes that the interest in spiritualism was evident in other European countries, including France and Germany. He elaborates on the reasons:
During and after the Great War, interest in the paranormal and the
after-life naturally deepened. It was inevitably and inextricably tied
up with the need to communicate with the fallen. One French observer
reversed the point. 'After a murderous war', he wrote, 'who would
doubt that the dead would try to communicate again?'18 This became a
key feature of the wartime and postwar appeal of spiritualism. It
provided a means through which the dead led the way. They helped both
to lift the burden of grief borne by their families and to spread the
'truth' of spirit communication.
Source: Jay Winter, 'Spiritualism and the ‘Lost Generation’. Chapter 3 in 'Spiritualism and the ‘Lost Generation’ (2014).
One piece of evidence in Britain is the increased membership of the Spiritualists' National Union, founded in 1901.
In 1914, there were 145 societies affiliated to the Spiritualists
National Union (SNU); by 1919 there were 309. In 1932, the newly
established Spiritualist and London based journal, Psychic News,
announced that there were 500 societies affiliated to the SNU.
Source: J. Hazelgrove, 'Spiritualism after the Great War', in 'Twentieth Century British History, Volume 10, Issue 4, 1999'
In addition, in the 1930s, there were large meetings held:
Both London and provincially based meetings were very popular. The
medium, Helen Hughes, regularly addressed an audience of 3,000 or
more, while 9,000 people gathered at the Royal Albert Hall to
witness Estelle Roberts speak to the dead.
Source: Hazelgrove
Further,
publications dealing with spirits and the spirit world were
undoubtedly popular. Sir Oliver Lodge's
Raymond (1916) and Arthur Conan Doyle's New Revelation (1918) and The Vital Message (1919) attained the status of Spiritualist classics in the interwar period. Perhaps the single most successful
publication was On the Edge of the Etheric (1931), by Arthur
Findlay....On the Edge of the Etheric was reprinted twenty-five
times between November 1931 and June 1932 and, according to Psychic
News, sold at the rate of 500 copies per week. In its first year of
publication the book ran to thirty impressions and was subsequently
translated into nineteen different languages.
Lodge's book, which related "the joy the author felt on contacting his own dead son" (Raymond was killed in 1915) became a best-seller, the author's knighthood and scientific reputation helping sales along even though the book was criticised for lacking credibility. Conan Doyle, another major celebrity in his time, frequently engaged in public debates and gave speeches on spiritualism.
The popularity of spiritualism was of some concern to established religion, although it wasn't simply a question of one or the other; beliefs often indicated a complicated mix of church teachings and spiritualist beliefs and stories. The Anglican church, with declining attendances, set up a committee to "investigate the subject of communications with discarnate spirits and the claims of Spiritualism in relation to the Christian Faith". Even during the war,
one chaplain told David Cairns, the Aberdeen theologian, 'The British
soldier has certainly got religion; I am not so sure, however, that he
has got Christianity.'
Source: Winter
The Catholic church was at least equally hostile:
...the distaste with which Catholicism traditionally viewed Spiritualism
was now accompanied by marked signs of anxiety, and special campaigns
were initiated to combat the perceived threat Spiritualism posed to
religious life. In 1926, a society called the Catholic Crusade Against
Spiritualism was formed. Its founders feared that Spiritualism
accounted 'for considerable leakage among Catholics', and proposed by
means of lectures to 'expose the dangers which follow upon the
practice of the cult'.
Source: Hazelgrove
Despite the exposing of many frauds, the most notorious perhaps being Helen Duncan, for many spiritualism connected in a way which provided them with comfort. As David Nash puts it, at the end of the war,
Some fervently sought a return to normality – to the comforting
certainties of the prewar world. But others exhibited a starkly
different outlook. They reasoned that it was those comforting
certainties, the very institutions that had dominated Britain in the
countdown to 1914, that had led the country into a catastrophic
conflict. Their reaction to the horrors of the war was to reject
rationality in favour of something altogether stranger, something that
encompassed witchcraft, spiritual renewal and communication with the
dead.
