However, hippos are even more endangered than the elephant; while there are 400,000 elephants left in the wild but just 130,000 hippos.
Auctioneers have seen an increased amount of interest in hippo ivory because of the legislation, as restorers worry about its effect on business.
James Lewis, a top auctioneer who has appeared on BBC show Flog It!, said: "There is an increase in interest in hippo ivory That interest isn't coming from carvers or people trying to make new pieces, [but] from restorers who are concerned about the legislation on the ivory content of antiques."
Campaigners have called on the Government to close the loophole to ensure the ban applies to all ivory-bearing animals. They have also warned that it is nearly impossible to tell whether a tusk is from a hippopotamus that was slaughtered recently or many years ago, and whether it was poached or legally killed.
Will Travers, president of the Born Free foundation, said authorities were "shifting pressure" on to hippos by only banning ivory from elephants. He said: "I sometimes can't tell the difference between different types of ivory and I've been in this for 35 years.
"It also gives illegal smugglers a cover. Go to Gatwick and ask them to tell the difference between a piece of elephant tusk and a piece of hippo tusk. They won't be able to. Hippos are already being negatively impacted. We have to have a blanket ban on ivory."
MPs and celebrities have asked Mr Gove to consider banning hippo ivory at the same time as elephant.
Zac Goldsmith said: "I'm proud that our government led the way in banning elephant ivory, but it's unfinished business. It would be a tragedy if efforts to protect elephants meant that other threatened species were targeted instead. We need to ban the trade in all ivory, whatever animal it's from."British hunters are also taking advantage of the fact they can legally bring back hippo carcasses as trophies.
Eduardo Goncalves, of the Campaign to Ban Trophy Hunting, said: "Despite being classed as vulnerable, hippos are the second most popular target animals among British trophy hunters. Over 350 trophies from hippos have been brought back into the UK over the past decade."