Six Nations tickets that appeared on the resale website Viagogo for inflated prices were leaked via local rugby clubs, it has emerged, prompting warnings that unfettered resale poses a threat to the game’s grassroots.

The Rugby Football Union told the Guardian that it sanctioned 57 clubs over ticket resale in 2018 alone and it is understood they have warned them that they risk being stripped of their allocation for international fixtures.

It comes after the Guardian revealed that more than a thousand tickets for the tournament had appeared on Viagogo for £370,000, despite resale restrictions that might lead to buyers being refused entry at the turnstile.

Subsequent inquiries have revealed that tickets are routinely being resold by members and corporate sponsors of local rugby clubs, which are allocated tickets by governing bodies.

Several Viagogo customers said they had received tickets that were clearly part of clubs’ initial allocations.

Judy Bowen paid £2,120.48 for four seats at Twickenham to see England v France, despite the tickets having a face value of £100 each. She said the final price due to be paid was unclear and she was even more shocked when later told by the RFU that the tickets were invalid and would be cancelled.

According to information printed on the tickets, they were initially allocated to Rosslyn Park, via the RFU’s system of distributing tickets to local rugby clubs. The south-west London club told the Guardian an internal investigation had discovered the tickets were issued to one of its corporate sponsors. “Club sponsors, along with members of Rosslyn Park, are reminded annually of the RFU and club’s policy on the resale of international tickets,” a spokesman said. “The corporate sponsor is now taking internal disciplinary action with the individual concerned.”

Bowen said the process of securing a refund from Viagogo, which she eventually managed, had been “more than a pain”.

Adam Dockery paid £4,612.82 for five tickets to see Ireland v England at the Aviva Stadium last weekend, despite the tickets having a face value of €110, only to be denied entry at the gate. He is still trying to secure a refund from Viagogo.

His tickets were initially allocated to Banbridge, in County Down, Northern Ireland, the same club where the Irish team’s captain, the hooker Rory Best, is registered.

A spokesman for the club said the member responsible for reselling their tickets on Viagogo had since had their access to tickets withdrawn. “Banbridge RFC are firmly against reselling of tickets and will withdraw access to tickets from any member found to have done so,” a spokesperson said.

The governing bodies of the countries taking part in the Six Nations typically issue a large proportion of tickets via rugby clubs, who then pass them on to their members. One source at a rugby club told the Guardian that members reselling tickets could threaten the very existence of the club. The source said if the RFU were to sanction the club by reducing or ending its allocation, it could suffer a membership fall‑off because some people join largely to gain access to international tickets.

An RFU spokesperson said: “If there is a suspicion that tickets are misused, this will initially be examined by the RFU. The club will be contacted to obtain an explanation, and the RFU will then decide on an appropriate sanction, if applicable, against set guidelines. This can result in a club losing some or all of its ticket allocation in subsequent seasons.”

Claire Turnham, who was awarded an MBE for her efforts in securing refunds for consumers through her Victim of Viagogo Facebook group, said: “As a rugby-loving Kiwi it’s devastating to realise the allocation of international tickets may be lost because of this appalling greed. Reselling is responsible for ripping the heart of the game at a grass roots level.”

Viagogo said: “The reason nobody can get a Six Nations ticket from the box office is because the RFU doesn’t make tickets available to the general public.”