Pre-war radios have been collected for years: Thirties Art Deco bakelite sets can fetch pounds 850 or so. But old televison sets have a strong claim to be the last major undiscovered collectable.
Mr Bennett-Levy's book lists every pre-war model worldwide. It is bound to start a race to rescue unrecognised collectors' pieces from attics, junk shops and auctions, especially in London - the only British city to receive pre-war television transmissions.
Before the rush comes, look out for any telly with a round cathode ray tube instead of the square ones that date from 1952. Big valves and transformers are another pre-war hallmark.
Mr Bennett-Levy, a dealer in mechanical music and early technology, cheerfully predicts that his numbered edition of 2,000 copies of Historic Televisions will raise collectors' prices beyond his own reach. He is not worried. During the past two years he has frenetically assembled at Monkton, his 16th-century fortified house near Edinburgh, a world-class collection of 65 sets, including 15 pre-war. He will sell the lot when the time is right, bringing joy to the bank manager who backed both his collecting and his publication costs.
Mr Bennett-Levy has located and catalogued 130 British pre-war sets and reckons there are probably about 200 more waiting to be discovered. Pre-war television was a luxury for the London rich. Sets cost as much as a family saloon car and HMV always sent round an engineer to install them. Some models were made only in single figures.
With great good fortune, you might unearth pre-war sets known to have been manufactured but of which there are no known examples. No pre-war Decca, Kostler Brandes, Bush or Scophony sets are known.
Pre-war projection sets - the image projected on to a big screen - are now virtually forgotten. No examples are known to have survived. Really intrepid telly sleuths might also try tracking down examples of pre-war German sets (used only in public viewing parlours), pre-war German automobile television and cable TV - or Baird's prototype colour sets of 1944.
The first key date for collectors is 1948. Models which pre-date the opening of the Birmingham transmitter that year are considered rare. Values decline after 1953, when sales were boosted by the Coronation. You can still buy Fifties models in provincial sales for a fiver. Standard converters to make the old 405-line system work will cost you under pounds 250. Then you can savour the smell of hot dust on valves. Bliss.
The bulk of the Bennett-Levy collection is in the attic of his home. In the cellar, past a massive pipe orchestrion once owned by the Maharaja of Ambala, lie the truly huge models. One is a Baird T14 of 1937 (the year after transmissions began) with radio, autochange gramophone and 'cellarette' (drinks cabinet) which, at an extra five guineas, brought the price to 130gns.
John Logie Baird, inventor of television, paid as much attention to commercial design as technology. The T14's 'mirror lid' reflects at 45 degrees from the horizontally mounted 15-inch screen - early tubes had to be installed upright because they were so long.
Mr Bennett-Levy paid pounds 1,000 for the T14 last year at Phillips, the London auctioneers. In the past two years only two pre-war sets have appeared at London auctions. Tony Jones, of Phillips Bayswater, considers it a coup that his next auction on 11 May (12 noon) will have three. Among them, a 1937 Marconiphone 703, a top-of-the-range radiogram, is estimated at pounds 600- pounds 800 but is expected to clear pounds 2,000.
Among more than 50 television sets from a props company auctioned by Academy Auctioneers of Ealing, west London, last month, Fifties Bush bakelites, classic collectables of the future, fetched up to pounds 150. Prices for rare sets are still 'ridiculously cheap', says Mr Bennett-Levy.
He began collecting after a video production company stopped ordering decorative old tellies from him but left him hooked. He had seen prices for early technology rise to pounds 8,500 for an Autophone cylinder jukebox and pounds 2,500 for a Stentophone compressed-air horn gramophone, both prices which the Science Museum paid him. But tellies?
In an enthusiastic foreword to the book, Malcolm McLeod, director of Glasgow's Hunterian Museum and Art Gallery, writes: 'Television is the most dominant mass communications medium of this or any other century, and one of the most pervasive cultural influences ever invented. For these reasons alone, every aspect of television merits serious study and critical evaluation.'
Mr Bennett-Levy was motivated by patriotism and nostalgia. Every British pre-war television had a screen coated with phosphors developed and manufactured by his grandfather, Dr Leonard Levy, whose research into phosphors kept British television, radar and X-rays pre-eminent throughout the world in the first half of this century. 'I felt that a fine collection of television sets would encapsulate all that was great in Great Britain,' he says.
There were some nailbiting moments. A Nottinghamshire dealer offered him a 1937, top-of-the-range HMV TV-radiogram, one of only 11 made, which he cheerfully refused, aware that he lacked the pounds 2,000 asked.
Then the familiar collector's nightmare set in. 'I told myself, 'Michael, you have just turned down a major example of Art Deco furniture. Are you serious about collecting?' '
He telephoned the dealer at 8.30 the following morning and bought it. Hours later the same dealer asked him whether he would like to make pounds 1,000 on it. He had been offered pounds 3,000. 'I could have made a profit of pounds 1,000 in 12 hours,' said Mr Bennett-Levy. 'But I told him to leave it where it was.' The HMV 902 became the cover illustration of his book.
His network of sources includes American collectors, UCLA's database, the commercial auction database of Thesaurus, the editor of the TV enthusiasts' magazine 405 Alive (circulation 250) and the findings of British intelligence sub-committee report 867 of 1946.
His trading methods are unusual. He prefers to buy 'sight unseen', trusting to Michael's Law: 'The quality of the purchase is inversely proportional to the distance travelled.' After publication day, five days hence, it looks as though Michael Bennett-Levy will not be straying far from Monkton House.
Historic Televisions and Video Recorders, pounds 12.95 ( pounds 15 overseas) inc p&p and update, from: MBL Publications, Monkton House, Old Craighall, Musselburgh, Midlothian EH21 8SF (031 665 5753).
405 Alive (TV nostalgia quarterly), annual subscription pounds 13 or sample copy pounds 3 (cheques payable to Andrew Emmerson) plus sae to: 71 Falcutt Way, Northampton, NN2 8PH.