English bookmakers have been hit hard on a low-key day by winning plunges on five horses, at least four of which are believed to have some link to legendary gambler and former trainer Barney Curley.

But leading firms were quick to downplay claims of a "multi-million pound bloodbath", with industry estimates put at around STG2 million ($A3.76 million).

Bookmakers had been on red-alert from early morning after latching on to the well-backed quintet, all of which were returning from lengthy absences and struck at Lingfield, Catterick and Kempton.

"It was a bad day at the office, nothing more and nothing less," a Ladbrokes spokesman said.

"Suggestions of a multi-million pound bloodbath are probably wide of the mark so we're not going to lunge for the violins just yet."

The first of the plunge horses was Eye Of The Tiger at Lingfield, who went off at even money and cruised to a nine-length win.

Now trained in Newmarket by Des Donovan, Eye Of The Tiger was a German Group Two winner but had not featured in seven starts for Curley.

The Lingfield stewards held an inquiry into the apparent improvement in form of Eye Of The Tiger.

Officials heard from Donovan, who said the horse had been in his care for seven months having previously been trained by Curley and its absence from the track was due to back problems and a near fore tendon injury.

Having heard his evidence, and received comments from the handicapper, the explanation was noted and Eye Of The Tiger was ordered to be routine tested.

Like Eye Of The Tiger, the Sophie Leech-trained Seven Summits was formerly with Curley and made a winning comeback in a hurdle at Catterick.

Indus Valley, also trained by Donovan, landed the third leg of the four in the perceived gamble at Kempton but the 4-6 shot had to work hard to collect.

Seamster was three lengths clear going into the final furlong but Kelly produced a power-packed drive to get the seven-year-old home by half a length on his first run for 700 days.

All eyes were on Low Key, trained by Curley's former assistant John Butler, in the final leg at Kempton and the seven-year-old made no mistakes at his first start since finishing last of seven in a race almost a year ago.

Quizzed by stewards, Butler said Low Key had been gelded since his last run and had benefited from the drop in class.

British Horseracing Authority spokesman Robin Mounsey said the situation had been monitored through the day.

"We were aware of, and have been monitoring, the situation today. In the cases of those horses who have shown an improvement in form an inquiry was held by the stipendiary stewards and all horses were routine tested," Mounsey said.

"It is BHA policy not to comment on specific investigations or speculation surrounding potential investigations, however an investigation would only occur if there is any evidence of Rules being breached."