By Lori Ewing

(Reuters) -Last week's landmark ruling on trans women in Britain will not impact Sunday's London Marathon, with race director Hugh Brasher saying he supports a recent World Athletics decision to gender test to "protect women's rights to compete fairly".

Brasher added he will wait for guidance from the Equality and Human Rights Commission (EHRC) and Sport England before deciding if changes are needed for future editions of the London Marathon, which currently permits runners in the mass race to self-identify their gender, but restricts entries in the elite and championship races to females at birth.

Last week's much anticipated ruling said only biological and not trans women meet the definition of a woman under equality laws, a decision that confirms that single-sex services for women such as sports can exclude trans women.

"It's really difficult to predict what we would do," Brasher said on a call with media on Wednesday.

"I've gone through loads of different scenario planning since the court delivered its verdict, but honestly, we have to wait until the commission gives its report, until Sport England do, because otherwise we're just going on to what ifs, what ifs, what ifs.

"We delight in being both inclusive but also protecting in competition the rights of women, which is incredibly important. Seb Coe and World Athletics have always led on that, and we absolutely look to continue doing that."

World Athletics president Coe announced last month that female athletes will soon have to undergo a one-time genetic test to compete in women's events, which has been met with criticism.

"I think that what World Athletics have done has been incredibly good for athletics and been really clear," Brasher said. "When you look at the Olympics, you're looking at protecting women's competitive sport, I think it's absolutely vital. The job that Seb Coe has done has put the sport at the forefront of protecting women's rights to compete fairly."

Asked how many trans athletes are entered in Sunday's marathon, Brasher said it is impossible to know, since it is self-selection.

"Your passport would say your gender, and your gender can say female, even if you were born male. And so this is where getting into the advice that there is going to be from the Equality and Human Rights Commission and Sport England is incredibly important," he said.

"This is complex. We're really clear about the competition element, anywhere where there is competition that includes 'good for age,' that has to be your biological birth sex."

(Reporting by Lori Ewing, editing by Pritha Sarkar)