Chuka Umunna was named as the spokesman for the newly formed Independent Group (TIG) as part of an announcement that saw all 11 of its MPs handed an organisational role or policy responsibility.

The former Labour MP said TIG had no immediate plans to appoint a leader as it was not yet a political party, adding that “all the members of our group have the right to be heard and a responsibility to provide leadership”.

Umunna had expressed his keenness to become leader last weekend, saying in a television interview that he hoped “to play the biggest role” in the breakaway group composed of eight Labour and three Tory MPs.

But for now he will take on a more modest spokesman role, leaving questions of leadership to one side until the group constitutes itself as a political party at some point before the end of the year.

Luciana Berger, who has been touted as another possible leader, will become spokesperson for home affairs, health, digital and culture; while the former Conservative Heidi Allen will take a welfare, social care and business brief.

Anna Soubry, a Conservative defector and former minister, will become Brexit spokeswoman, while Chris Leslie, a longtime ally of Umunna and a former shadow chancellor, will take the economic brief. The positions were announced in alphabetical order.

Anna Soubry, the former Tory MP, will become Brexit spokeswoman for the Independent Group. Photograph: Jonathan Hordle/ITV/REX/Shutterstock

TIG has had a mixed first full week in Westminster. A second referendum motion its members put down was not accepted by the Speaker, John Bercow, in Wednesday’s Brexit debate.

Berger was not selected at prime minister’s questions by Bercow earlier on Wednesday despite hoping to be called on to quiz Theresa May.

But a YouGov poll placed TIG at 18%, five points behind Labour, its highest rating in first voting surveys since its emergence at the beginning of last week. Other polls have put TIG at lower levels, an Opinium poll published in the Observer last weekend put the new grouping at 6%.

Angela Smith, who was forced to apologise after referring to people from black, Asian and minority ethnic backgrounds as having a “funny tinge”, is taking on a broad portfolio including transport, local government and housing, energy and environment.

Sarah Wollaston, the former Conservative GP turned MP, has not taken on a policy brief but has instead taken on responsibility for new members. The group has said it wants to introduce a procedure for admitting people.

Allen had previously said that she did not want TIG to become a home for “waifs and strays” such as the MPs John Woodcock and Ivan Lewis, both of whom left Labour with harassment allegations unresolved.

The appointments follow a series of meetings this week. On Monday, Gavin Shuker, the former Labour MP who represents Luton South, was named as group convenor, who will organise its meetings. Insiders have indicated that donations to the group already total in “the hundreds of thousands” of pounds.